Plasma lamp with conductive material positioned relative to RF feed

ABSTRACT

In an example embodiment, an electrodeless plasma lamp is provided which comprises a lamp body comprising a dielectric material having a relative permittivity greater than 2, and a bulb adjacent to the lamp body, the bulb containing a fill that forms a plasma when RF power is coupled to the fill from the lamp body. An RF feed is coupled to the lamp body and a radio frequency (RF) power source for coupling power into the lamp body through the RF feed is provided. A shortest distance between an end of the bulb and a point on the RF feed traverses at least one electrically conductive material of the lamp body.

CROSS-REFERENCE

This application claims benefit of priority to U.S. ProvisionalApplication Ser. No. 60/730,785 filed on Oct. 27, 2005 (2447.005PRV),U.S. Provisional Application Ser. No. 60/730,654 filed on Oct. 27, 2005(2447.004PRV), U.S. Provisional Application Ser. No. 60/730,720 filed onOct. 27, 2005 (2447.006PRV), U.S. Provisional Application Ser. No.60/730,950 filed on Oct. 27, 2005 (2447.007PRV), U.S. ProvisionalApplication Ser. No. 60/730,953 filed on Oct. 27, 2005 (2447.008PRV) andU.S. Provisional Application Ser. No. 60/730,786 filed on Oct. 27, 2005(2447.009PRV), the entire contents of which are herein incorporated byreference.

BACKGROUND

I. Field

The field of the present invention relates to devices and methods forgenerating light, and more particularly to electrodeless plasma lamps.

II. Background

Electrodeless plasma lamps may be used to provide point-like, bright,white light sources. Because electrodes are not used, they may havelonger useful lifetimes than other lamps. Some plasma lamps directmicrowave energy into an air cavity, with the air cavity enclosing abulb containing a mixture of substances that can ignite, form a plasma,and emit light. However, for many applications, light sources that arebrighter, smaller, less expensive, more reliable, and have longer usefullifetimes are desired.

Plasma lamps have been proposed that use a dielectric waveguide body toreduce the size of the lamp. See, for example, U.S. Pat. No. 6,737,809B2 and U.S. Pat. No. 6,922,021. An example lamp of this type may use asolid dielectric waveguide body in the shape of a rectangular prism orcylinder such as shown in FIGS. 1A and 1B, respectively. An amplifiercircuit (AC1, AC2) may be used to provide power to the waveguide body(WB1, WB2) to excite a plasma in a bulb (PB1, PB2) positioned within alamp chamber (LC1, LC2) in the waveguide body (WB1, WB2).

It may be desirable to reduce the operating frequency for certainapplications, so as to reduce the cost of the associated lampelectronics. Because of the wide availability and relatively low cost ofparts, operation in the 900 MHz band commonly used for consumerelectronics is particularly desirable. Another band of interest isaround 2 GHz which in recent years has been widely utilized forstate-of-the-art consumer electronics.

One way of reducing frequency is to use materials with a high dielectricconstant. However, many such materials suffer from both low thermalconductivity and poor resistance to heat-induced stress, making thempoorly suited for a plasma lamp waveguide body. Moreover, some highdielectric constant materials suffer large changes in dielectricconstant over the operational temperature range of a plasma lamp.

What is desired are improved plasma lamp configurations, and methodstherefor, which can operate at the low end of the microwave frequencyrange without incurring the size penalty caused by lowering frequency,and which facilitate adjustment of resonant mode frequencies within aselected band. What is also desired are improved plasma lampconfigurations, and methods therefor, which allow for a reduced size tobe used for operation at a desired frequency. What is also desired areimproved bulb and lamp configurations and methods for providing highbrightness. What is also desired are improved configurations and methodsfor ignition, power control and thermal management.

SUMMARY

In an example embodiment, an electrodeless plasma lamp is provided whichcomprises a lamp body comprising a dielectric material having a relativepermittivity greater than 2 and a bulb adjacent to the lamp body, thebulb containing a fill that forms a plasma when RF power is coupled tothe fill from the lamp body. The lamp further comprises an RF feedcoupled to the lamp body, a radio frequency (RF) power source forcoupling power into the lamp body through the RF feed is also provided.A shortest distance between an end of the bulb and a point on the RFfeed traverses at least one electrically conductive material of the lampbody.

The bulb may have an exposed end from which light exits the plasma lamp,and a concealed end, the shortest distance being between the concealedend of the bulb and the RF feed.

In a further example embodiment, an electrodeless plasma lamp isprovided which comprises a lamp body comprising a dielectric materialhaving a relative permittivity greater than 2 and a bulb adjacent to thelamp body, the bulb containing a fill that forms a plasma when RF poweris coupled to the fill from the lamp body. A first RF feed may becoupled to the lamp body to provide radio frequency (RF) power and asecond RF feed may be coupled to the lamp body to obtain feedback fromthe lamp body. An RF power source for coupling power into the lamp bodythrough the RF feed is provided wherein the RF power source isconfigured to provide RF power at a frequency that is within theresonant bandwidth of a resonant mode for the lamp body. A distance froman end of the second RF feed to a mid-point of the first RF feedtraverses at least a first electrically conductive material of the lampbody.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of example embodiments will be obtained by reference to thefollowing detailed description and the accompanying drawings in which:

FIG. 1A schematically depicts a plasma lamp according to the prior art,including a rectangular prism-shaped waveguide body of dielectricmaterial.

FIG. 1B schematically depicts a plasma lamp according to the prior art,including a cylindrical-shaped waveguide body of dielectric material.

FIG. 2 is a perspective sectional view of a cylindrical dielectricwaveguide body according to a first example embodiment of the invention,including an opening separated from a bottom recess by a layer ofdielectric material.

FIG. 3 is a perspective sectional view of a rectangular prism-shapeddielectric waveguide body according to a second example embodiment,including an opening separated from a bottom recess by a layer ofdielectric material.

FIG. 4A is a cross-sectional view of the FIG. 2 waveguide body with abulb in the opening, taken along line 4A-4A of FIG. 2.

FIG. 4B is a cross-sectional view of the FIG. 3 waveguide body with abulb in the opening, taken along line 4B-4B of FIG. 3.

FIG. 4C schematically depicts a plasma lamp according to the first orsecond example embodiment wherein the dielectric waveguide body isconnected to an amplifier, and an external microprocessor controls theamplifier and a phase-shifter.

FIGS. 4D, 4E, 4F, 4G, 4H, 4I, 4J and 4K show example bulb configurationsthat may be used in connection with example embodiments.

FIG. 5 is a perspective sectional view of a cylindrical dielectricwaveguide body according to a third example embodiment, including acylindrical opening in communication with a bottom recess.

FIG. 6 is a perspective sectional view of a rectangular prism-shapeddielectric waveguide body according to a fourth example embodiment,including a cylindrical opening in communication with a bottom recess.

FIG. 7A is a cross-sectional view of the FIG. 5 waveguide body with abulb in the opening, taken along line 7A-7A of FIG. 5.

FIG. 7B is a cross-sectional view of the FIG. 6 waveguide body with abulb in the opening, taken along line 7B-7B of FIG. 6.

FIG. 7C schematically depicts a plasma lamp according to the third orfourth example embodiment wherein the dielectric waveguide body isconnected to an amplifier, and an external microprocessor controls theamplifier and a phase-shifter.

FIG. 8 is a perspective sectional view of a cylindrical dielectricwaveguide body according to a fifth example embodiment, including a toprecess, a bottom recess, and a cylindrical opening in communication withthe top and bottom recesses.

FIG. 9 is a perspective sectional view of a rectangular prism-shapeddielectric waveguide body according to a sixth example embodiment,including a top recess, a bottom recess, and a cylindrical opening incommunication with the top and bottom recesses.

FIG. 10A is a cross-sectional view of the FIG. 8 waveguide body with abulb in the opening, taken along line 10A-10A of FIG. 8.

FIG. 10B is a cross-sectional view of the FIG. 9 waveguide body with abulb in the opening, taken along line 10B-10B of FIG. 9.

FIG. 10C schematically depicts a plasma lamp according to the fifth orsixth example embodiment wherein the dielectric waveguide body isconnected to an amplifier, and an external microprocessor controls theamplifier and a phase-shifter.

FIG. 11 shows dimensional parameters of the FIG. 4A, 4B, 7A or 7Bcross-sections used in finite element model (FEM) simulations of theelectric field intensity in the FIG. 2, 3, 5 or 6 waveguide body.

FIG. 12A shows the FEM-simulated electric field intensity in the FIG. 5waveguide body designed for operation at 900 MHz and resonating at thebody's fundamental mode frequency.

FIG. 12B shows the FEM-simulated electric field intensity in the FIG. 5waveguide body designed for operation at 2.15 GHz and resonating at thebody's fundamental mode frequency.

FIG. 13A shows the sensitivity of the fundamental mode frequency of theFIG. 5 waveguide body, designed for operation at 900 MHz, to dimensionalparameter g₀ (see FIG. 11) for fixed body thickness and cylinderdiameter, and fixed recess diameter and opening diameter.

FIG. 13B shows the sensitivity of the fundamental mode frequency of theFIG. 5 waveguide body, designed for operation at 2.15 GHz, todimensional parameter g₀ for fixed body thickness and cylinder diameter,and fixed recess diameter and opening diameter.

FIG. 14A shows the diameter of a cross section of a cylindricalwaveguide body according to an example embodiment.

FIG. 14B shows the diagonal of a cross section of a rectangularwaveguide body according to an example embodiment.

FIG. 14C shows the maximum distance between two points in a cylindricalwaveguide body according to an example embodiment.

FIG. 14D shows the maximum distance between two points in a rectangularwaveguide body according to an example embodiment.

FIG. 15A is a graph showing the ratio of diameter over wavelength as afunction of frequency for shaped waveguides according to exampleembodiments and for a cylindrical waveguide.

FIG. 15B is a graph showing the ratio of diagonal over wavelength as afunction of frequency for shaped waveguides according to exampleembodiments and for a rectangular waveguide.

FIG. 16A compares, as a function of body diameter, the fundamental modefrequency of the FIG. 5 waveguide body with that of a cylindrical FIG.1B waveguide body, when both are designed for operation at 2 GHz.

FIG. 16B plots the FIG. 16A data as the ratio of the FIG. 1B bodydiameter to the FIG. 5 body diameter, as a function of fundamental modefrequency.

FIG. 17A compares, as a function of body volume, the fundamental modefrequency of the FIG. 5 waveguide body with that of a cylindrical FIG.1B waveguide body, when both are designed for operation at 2 GHz.

FIG. 17B plots the FIG. 17A data as the ratio of the FIG. 1B body volumeto the FIG. 5 body volume, as a function of fundamental mode frequency.

FIG. 18A compares, as a function of body diagonal, the fundamental modefrequency of the FIG. 6 waveguide body with that of a rectangular prismFIG. 1A waveguide body, when both are designed for operation at 2 GHz.

FIG. 18B plots the FIG. 18A data as the ratio of the FIG. 1A bodydiagonal to the FIG. 6 body diagonal, as a function of fundamental modefrequency.

FIG. 19A compares, as a function of body volume, the fundamental modefrequency of the FIG. 6 waveguide body with that of a rectangular FIG.1A waveguide body, when both are designed for operation at 2 GHz.

FIG. 19B plots the FIG. 19A data as the ratio of the FIG. 1A body volumeto the FIG. 6 body volume, as a function of fundamental mode frequency.

FIG. 20A compares, as a function of body diameter, the fundamental modefrequency of the FIG. 5 waveguide body with that of a cylindrical FIG.1B waveguide body, when both are designed for operation at 1 GHz.

FIG. 20B plots the FIG. 20A data as the ratio of the FIG. 1B bodydiameter to the FIG. 5 body diameter, as a function of fundamental modefrequency.

FIG. 21A compares, as a function of body volume, the fundamental modefrequency of the FIG. 5 waveguide body with that of a cylindrical FIG.1B waveguide body, when both are designed for operation at 1 GHz.

FIG. 21B plots the FIG. 21A data as the ratio of the FIG. 1B body volumeto the FIG. 5 body volume, as a function of fundamental mode frequency.

FIG. 22A compares, as a function of body diagonal, the fundamental modefrequency of the FIG. 6 waveguide body with that of a rectangular prismFIG. 1A waveguide body, when both are designed for operation at 1 GHz.

FIG. 22B plots the FIG. 22A data as the ratio of the FIG. 1A bodydiagonal to the FIG. 6 body diagonal, as a function of fundamental modefrequency.

FIG. 23A compares, as a function of body volume, the fundamental modefrequency of the FIG. 6 waveguide body with that of a rectangular FIG.1A waveguide body, when both are designed for operation at 1 GHz.

FIG. 23B plots the FIG. 23A data as the ratio of the FIG. 1A body volumeto the FIG. 6 body volume, as a function of fundamental mode frequency.

FIG. 24 is a cross-sectional view of a cylindrical or rectangularprism-shaped waveguide body according to a seventh example embodiment,including a bulb within an opening within a sleeve of high thermalconductivity material within a dielectric waveguide body.

FIG. 25 is a cross-sectional view of a cylindrical or rectangularprism-shaped waveguide body according to an eighth example embodiment,including a bulb within an opening within a sleeve of high thermalconductivity material within a dielectric waveguide body having a bottomrecess.

FIG. 26 is a cross-sectional view of a lamp with a waveguide bodyaccording to a ninth example embodiment.

FIG. 27A is a side view of a lamp according to an example embodimentwith a connector to a drive probe and a connector to a feedback probeaccording to an example embodiment.

FIG. 27B is a chart illustrating coupling between a port for a driveprobe and a port for a feedback probe for the lamp of FIG. 27A as afunction of frequency during periods of lamp operation from ignition tosteady state.

FIG. 27C is a flow chart of a method for operating a lamp according toan example embodiment.

FIG. 27D is a flow chart of a method for brightness adjustment accordingto an example embodiment.

FIG. 28 is a cross-sectional view of a lamp with a waveguide bodyaccording to a tenth example embodiment.

FIG. 29 is a cross-sectional view of a lamp with a waveguide bodyaccording to an example eleventh embodiment.

FIGS. 30A and 30B are perspective views of a back plate and heat sinkassembly according to an example embodiment.

DETAILED DESCRIPTION

While the present invention is open to various modifications andalternative constructions, the example embodiments shown in the drawingswill be described herein in detail. It is to be understood, however,there is no intention to limit the invention to the particular formsdisclosed. On the contrary, it is intended that the invention cover allmodifications, equivalences and alternative constructions falling withinthe spirit and scope of the invention as expressed in the appendedclaims.

FIG. 2 is a perspective sectional view of a cylindrical waveguide body40 according to a first example. Body 40 includes dielectric materialhaving a dielectric constant greater than about 2. For example, alumina,a ceramic having a dielectric constant of about 9, may be used. In someexample embodiments, the dielectric material may have a dielectricconstant in the range of from 2 to 10 or any range subsumed therein, ora dielectric constant in the range from 2 to 20 or any range subsumedtherein, or a dielectric constant in the range from 2 to 100 or anyrange subsumed therein, or an even higher dielectric constant. In someexample embodiments, the body 40 may include more than one suchdielectric material resulting in an effective dielectric constant forthe body 40 within any of the ranges described above. Body 40 has acylindrical outer surface 40S, a planar upper surface 40U from whichdepends downwardly an opening 42 for receiving a bulb, determined by acircumferential surface 42S and a planar bottom surface 42B, and aplanar lower surface 40L from which depends upwardly a recess 44determined by a circumferential surface 44S and a planar top surface44T. A layer 46 of dielectric material separates chamber bottom surface42B from recess top surface 44T. Surfaces 42S and 44S are cylindrical;however, other symmetric shapes, such as square or rectangular prisms,and asymmetric shapes may be used. The axis of symmetry of body 40coincides with that of opening 42 and recess 44; however, bodyconfigurations with offset axes also are feasible. Surfaces 40S, 40U and40L may be coated with an electrically conductive coating, as maysurfaces 42S and 42B of opening 42 and surfaces 44S and 44T of recess44. In example embodiments, the coating may be metallic electroplating.In other example embodiments, the coating may be silver paint or othermetallic paint. The paint may be brushed or sprayed onto the waveguidebody 40 and may be fired or cured at high temperature. First and secondopenings 48A, 48B extend from surface 40L into body 40, on oppositesides of recess 44. As shown in FIG. 4A, a cross-sectional view of body40 taken along line 4A-4A of FIG. 2, a plasma bulb 50, positioned withinopening 42. The plasma bulb 50 may have an outer surface 50S whosecontour matches that of surface 42S and be separated from surface 42S bya layer 49 of heat-sintered alumina powder or adhesive. Layer 49 may beused to optimize thermal conductivity between the bulb surface 50S andthe waveguide body 40. Alternatively, surfaces 42S and 50S are separatedby an air-gap. First and second probes 52, 54 are positioned,respectively, within openings 48A, 48B. In some example embodimentshaving a body such as body 40, at least one additional probe may bepositioned in the body 40.

FIG. 3 is a perspective sectional view of a rectangular prism-shapedwaveguide body 60 according to a second example embodiment. Body 60includes dielectric material having a dielectric constant greater thanabout 2, for example, alumina. In some example embodiments, thedielectric material may have a dielectric constant in the range of from2 to 10 or any range subsumed therein, or a dielectric constant in therange from 2 to 20 or any range subsumed therein, or a dielectricconstant in the range from 2 to 100 or any range subsumed therein, or aneven higher dielectric constant. In some example embodiments, the body60 may include more than one such dielectric material resulting in aneffective dielectric constant for the body within any of the rangesdescribed above. Body 60 has opposed planar first and second outersurfaces 60A, 60B (not shown), respectively, orthogonal to opposedplanar third and fourth outer surfaces 60C, 60D. Body 60 further has aplanar upper surface 60U from which depends downwardly an opening 62 forreceiving a bulb, determined by a circumferential surface 62S and aplanar bottom surface 62B, and a planar lower surface 60L from whichdepends upwardly a recess 64 determined by a circumferential surface 64Sand a planar top surface 64T. A layer 66 of dielectric materialseparates chamber bottom surface 62B from recess top surface 64T.Surfaces 62S and 64S are cylindrical; however, other symmetric shapes,such as square or rectangular prisms, and asymmetric shapes may be used.The axis of symmetry of body 60 coincides with that of opening 62 andrecess 64; however, body configurations with offset axes also arefeasible. Surfaces 60A, 60B, 60C, 60D and/or 60U and 60L may be coatedwith an electrically conductive coating, such as silver paint or othermetallic coating as described above, as may surfaces 62S and 62B ofopening 62 and surfaces 64S and 64T of recess 64. As shown in FIG. 4B, across-sectional view of body 60 taken along line 4B-4B of FIG. 3, aplasma bulb 70, may be positioned within opening 62. The plasma bulb 70may have an outer surface 70S whose contour matches that of surface 62Sand be separated from the surface 62S by a layer 69 of heat-sinteredalumina powder or adhesive. The layer 69 may be used to optimize thermalconductivity between the bulb surface 70S and the waveguide body 60.Alternatively, surfaces 62S and 70S are may be separated by an air-gap.First and second probes 72, 74 are may be positioned, respectively,within openings 68A, 68B extending from surface 60L into body 60, onopposite sides of recess 64. In some example embodiments having a bodysuch as body 60, at least one additional probe may be positioned in thebody 60.

As depicted schematically in FIG. 4C, a plasma lamp PL1, PL2 accordingto the first or second example embodiment, respectively, includes anamplifier AM1 whose output is connected to the first (drive) probe andwhose input is connected to the second (feedback) probe through anactive phase-shifter PS1 which modifies the phase of the signal from thesecond probe. An example implementation utilizes a PS214-315voltage-controlled phase-shifter available commercially from SkyworksSolutions Inc. of Woburn, Mass. The amplifier AM1 and phase-shifter PS1may be controlled by a microprocessor MP1 or other controller whichcoordinates the lamp startup and shutdown sequences and optimizes theloop phase during startup. In example embodiments, the amplifier AM1 maygenerate power at a frequency in the range of about 50 MHz (0.05 GHz) toabout 30 GHz.

FIGS. 4D, 4E, 4F, 4G, 4H, 4I, 4J and 4K show example bulb configurationsthat may be used in connection with example embodiments. FIG. 4D shows aside cross section of a cylindrical bulb 400 having planar top 402 andbottom 404 surfaces. FIG. 4E shows a top view of a cross section throughthe middle of bulb 400. In this example, the cross section is circular,although rectangular or irregular shaped cross sections may be used insome example embodiments (e.g., hourglass shaped bulbs). FIG. 4F shows aside cross section of an oval bulb 406 having curved top 408 and bottom410 surfaces. FIG. 4G shows a top view of a circular cross sectionthrough the middle of bulb 406. FIG. 4H shows a side cross section of acylindrical bulb 412 having hemisphere shaped top 414 and bottom 416surfaces. FIG. 4I shows a top view of a circular cross section throughthe middle of bulb 412. FIG. 4J shows a side cross section of aspherical bulb 418. FIG. 4K shows a top view of a cross section throughthe middle of spherical bulb 418. These shapes are examples only andother shapes may be used as well such as parabolically contoured bulbsor irregularly shaped bulbs (e.g., hourglass shaped bulbs).

Each of the above example bulbs has a length L between the inside wallsof the bulb and an outer length OL. Each of the bulbs also has a width Wbetween the inside walls of the bulb and an outer width OW. In bulbswith circular cross sections, the width W is equal to the inner diameterof the bulb and the outer width OW is equal to the outer diameter of thebulb. In a spherical bulb as show in FIGS. 4J and 4K the length andwidth are both equal to the diameter. For irregular shaped bulbs, theinner width may be determined by using the largest interior width in theregion where power is predominantly coupled into the bulb and the innerlength may be determined using the greatest length between distal endsof the bulb.

In example embodiments, the bulb may be in any of the above shapes orother shapes and have, for example, an outer width OW in a range between2 and 30 mm or any range subsumed therein, an inner width W in a rangebetween 1 and 25 mm or any range subsumed therein, a wall thickness in arange between 0.5 and 4 mm or any range subsumed therein, an innerlength L between 4 and 20 mm or any range subsumed therein. In exampleembodiments, the bulb volume may be between 10.47 mm³ and 750 mm³ or anyrange subsumed therein. The above dimensions are examples only and bulbswith other dimensions may also be used in example embodiments. In aparticular example, the bulb may have a shape as shown in FIGS. 4H and4I with an inner width of 3 mm, an inner length of 9 mm and a volume ofabout 56.52 mm³. This example bulb may have an outer height of 14 mm, anouter width of 6 mm and have the inner volume that is closer to the topby 1 mm than the bottom (e.g., the thickness of the wall at the lowerhemisphere is about 3 mm thick and the thickness of the wall at the topis about 2 mm thick). In another example, the bulb may have a shape asshown in FIGS. 4H and 4I with an inner width of 2 mm, an inner length of4 mm and a volume of about 10.47 mm³.

Example bulbs in any of the above configurations may comprise anenvelope of transmissive material such as quartz, sapphire or othersolid dielectric. Example bulbs may also be formed by a combination ofmaterials forming an envelope. For example, a reflective body of ceramicmay have an opening covered by a transmissive window of quartz, sapphireor transmissive material. Some bulbs may also be formed in part bysurfaces of the waveguide body and/or other surfaces of a lamp body. Forexample, a lamp chamber may be formed in the waveguide body and coveredby a transmissive window of quartz, sapphire or transmissive material.

FIG. 5 is a perspective sectional view of a cylindrical waveguide body80 according to a third example embodiment. Body 80 includes dielectricmaterial having a dielectric constant greater than about 2, for example,alumina. In some embodiments, the dielectric material may have adielectric constant in the range of from 2 to 10 or any range subsumedtherein, or a dielectric constant in the range from 2 to 20 or any rangesubsumed therein, or a dielectric constant in the range from 2 to 100 orany range subsumed therein, or an even higher dielectric constant. Insome example embodiments, the body 80 may include more than one suchdielectric material resulting in an effective dielectric constant forthe body 80 within any of the ranges described above. Body 80 has acylindrical outer surface 80S, a planar upper surface 80U, and a planarlower surface 80L from which depends upwardly a recess 82 determined bya circumferential surface 82S and a planar top surface 82T. An opening84, determined by a circumferential surface 84S and effectively forminga lamp chamber, extends between surfaces 80U and 82T so that the opening84 is in communication with recess 82. Surfaces 82S and 84S arecylindrical; however, other symmetric shapes, such as square orrectangular prisms, and asymmetric shapes may be used. The axis ofsymmetry of body 80 coincides with that of recess 82 and opening 84;however, body configurations with offset axes also are feasible.Surfaces 80S, 80U and 80L may be coated with an electrically conductivecoating, such as silver paint or other metallic coating as describedabove, as may surface 84S of opening 84 and surfaces 82S and 82T ofrecess 82. First and second openings 86A, 86B extend from surface 80Linto body 80, on opposite sides of recess 82. As shown in FIG. 7A, across-sectional view of body 80 taken along line 7A-7A of FIG. 5, aplasma bulb 90 (see FIG. 7A) may be closely received within opening 84.The plasma bulb 90 may have an outer surface 90S whose contour matchesthat of surface 84S and is separated from surface 84S by a layer 88 ofheat-sintered alumina powder or adhesive. Layer 88 may be used tooptimize thermal conductivity between the bulb surface 90S and thewaveguide body 80. Alternatively, surfaces 84S and 90S may be separatedby an air-gap. Bulb 90 has upper and lower ends 90U, 90L, respectively,which extend, respectively, above body upper surface 80U and belowrecess top surface 82T, into recess 82. Thus, in this example embodimentthe bulb 90 ends are not enclosed by body 80 and are exposed to theexternal environment, permitting efficient radiation of thermal energyfrom the plasma whose peak temperature can range from 3000° to 10,000°C.

As can be inferred from the example electric field intensitydistributions shown in FIGS. 12A and 12B, the bulb ends 90U, 90L wouldbe exposed only to regions of reduced electric field intensity,resulting in longer bulb lifetime due to reduced plasma impingement onthem. In other example embodiments the bulb 90 may be positionedcompletely within the opening 84. First and second probes 92, 94 may bepositioned, respectively, within openings 86A, 86B. In some exampleembodiments having a body such as body 80, at least one additional probemay be positioned in the body.

FIG. 6 is a perspective sectional view of a rectangular prism-shapedwaveguide body 100 according to a fourth example embodiment. Body 100includes dielectric material having a dielectric constant greater thanabout 2, for example, alumina. In some embodiments, the dielectricmaterial may have a dielectric constant in the range of from 2 to 10 orany range subsumed therein, or a dielectric constant in the range from 2to 20 or any range subsumed therein, or a dielectric constant in therange from 2 to 100 or any range subsumed therein, or an even higherdielectric constant. In some example embodiments, the body 100 mayinclude more than one such dielectric material resulting in an effectivedielectric constant for the body 100 within any of the ranges describedabove. Body 100 has opposed planar first and second outer surfaces 100A,100B (not shown), respectively, orthogonal to opposed, planar third andfourth outer surfaces 100C, 100D. Body 100 further has a planar uppersurface 100U, and a planar lower surface 100L from which dependsupwardly a recess 102 determined by a circumferential surface 102S and aplanar top surface 102T. An opening 104, determined by a circumferentialsurface 104S and effectively forming a lamp chamber, extends betweensurfaces 100U and 102T so that the opening 104 is in communication withrecess 102. Surfaces 102S and 104S are cylindrical; however, othersymmetric shapes, such as square or rectangular prisms, and asymmetricshapes may be used. The axis of symmetry of body 100 coincides with thatof recess 102 and opening 104, but body configurations with offset axesalso are feasible. Surfaces 100A, 100B, 100C, 100D and/or 100U and 100Lmay be coated with an electrically conductive coating, such as silverpaint or other metallic coating as described above, as may surface 104Sof opening 104 and surfaces 102S and 102T of recess 102. First andsecond openings 106A, 106B extend from surface 100L into body 100, onopposite sides of recess 102. As shown in FIG. 7B, a cross-sectionalview of body 100 taken along line 7B-7B of FIG. 6, a plasma bulb 110 maybe positioned within opening 104. The plasma bulb 110 may have an outersurface 110S whose contour matches that of surface 104S is separatedfrom surface 104S by a layer 108 of heat-sintered alumina powder oradhesive. Layer 108 may be used to optimize thermal conductivity betweenthe bulb surface 110S and the waveguide body 100. Alternatively,surfaces 104S and 110S are may be separated by an air-gap. Bulb 110 hasupper and lower ends 110U, 110L which extend, respectively, above bodyupper surface 100U and below recess top surface 102T. Thus, in thisexample embodiment the bulb ends are exposed to the external environmentand to regions of reduced electric field intensity. In some exampleembodiments, the recess 102 may also be filled with alumina powder(which may be heat sintered) or other ceramic or solid dielectric. Thematerial filling the recess 102 may provide a reflective surface aroundthe lower end of the bulb 110. In these example embodiments, thematerial filling the recess 102 may be separated from the waveguide body100 by the electrically conductive coating on the surface of thewaveguide so the lower end of the bulb 110 is still in a region ofreduced electric field intensity relative to the portion of the bulbsurrounded by the waveguide body 100. In other example embodiments thebulb 110 may be positioned completely within the opening 104. First andsecond probes 112, 114 are positioned, respectively, within openings106A, 106B. In some example embodiments having a body such as body 100,at least one additional probe may be positioned in the body.

As depicted schematically in FIG. 7C, a plasma lamp PL3, PL4 accordingto the third or fourth example embodiment, respectively, may include anamplifier AM2 whose output is connected to the first (drive) probe andwhose input is connected to the second (feedback) probe through anactive phase-shifter PS2 which modifies the phase of the signal from thesecond probe The amplifier AM2 and phase-shifter PS2 may be controlledby a microprocessor MP2 or other controller which coordinates the lampstartup and shutdown sequences and optimizes the loop phase duringstartup. In example embodiments, the amplifier AM2 may generate power ata frequency in the range of about 50 MHz to about 30 GHz or any rangesubsumed therein.

FIG. 8 is a perspective sectional view of a cylindrical waveguide body120 according to a fifth example embodiment. Body 120 includesdielectric material having a dielectric constant greater than about 2,for example, alumina. In some example embodiments, the dielectricmaterial may have a dielectric constant in the range of from 2 to 10 orany range subsumed therein, or a dielectric constant in the range from 2to 20 or any range subsumed therein, or a dielectric constant in therange from 2 to 100 or any range subsumed therein, or an even higherdielectric constant. In some example embodiments, the body 120 mayinclude more than one such dielectric material resulting in an effectivedielectric constant for the body 120 within any of the ranges describedabove. Body 120 has a cylindrical outer surface 120S, and a planar uppersurface 120U from which depends downwardly an upper recess 122determined by a circumferential surface 122S and a planar bottom surface122B. Body 120 further has a planar lower surface 120L from whichdepends upwardly a lower recess 124 determined by a circumferentialsurface 124S and a planar top surface 124T. An opening 126, determinedby a circumferential surface 126S and effectively forming a lampchamber, extends between surfaces 122B and 124T so that the opening 126is in communication with recesses 122 and 124. Surfaces 122S, 124S and126S are cylindrical; however, other symmetric shapes such as square orrectangular prisms, and asymmetric shapes may be used. The axis ofsymmetry of body 120 coincides with that of upper recess 122, opening126 and lower recess 124; however, body configurations with offset axesalso are feasible. Surfaces 120S, 120U and 120L may be coated with anelectrically conductive coating, such as silver paint or other metalliccoating as described above, as may surfaces 122S and 122B of upperrecess 122, surface 126S of opening 126, and surfaces 124S and 124T oflower recess 124. First and second openings 128A, 128B extend fromsurface 120L into body 120, on opposite sides of lower recess 124. Asshown in FIG. 10A, a cross-sectional view of body 120 taken along line10A-10A of FIG. 8, a plasma bulb 130 may be closely received within theopening 126. The plasma bulb 130 is shown to have an outer surface 130Swhose contour matches that of surface 126S and is separated from surface126S by a layer 132 of heat-sintered alumina powder or adhesive. Layer132 may be used to optimize thermal conductivity between the bulbsurface 130S and the waveguide body 120. Alternatively, surfaces 126Sand 130S are may be separated by an air-gap. Bulb 130 has upper andlower ends 130U, 130L, respectively, which extend, respectively, abovebottom surface 122B of upper recess 122 and below top surface 124T oflower recess 124. Because the bulb ends 130U, 130L protrude,respectively, into upper and lower recesses 122, 124, they are notexposed to the highest temperatures generated by the plasma. As evidentfrom FIG. 10A, because the waveguide body 120 is not proximate to thebulb ends 130U, 130L, they are exposed only to regions of reduced fieldintensity. In some example embodiments, the lower recess 124 may also befilled with alumina powder (which may be heat sintered) or other ceramicor solid dielectric. The material filling the lower recess 124 mayprovide a reflective surface around the lower end of the bulb 130. Inthese example embodiments, the material filling the lower recess 124 maybe separated from the waveguide body 120 by the electrically conductivecoating on the surface of the waveguide so the lower end 130L of thebulb 130 is still in a region of reduced electric field intensityrelative to the portion of the bulb 130 surrounded by the waveguide body120. In other example embodiments the bulb ends 130U, 130L do notprotrude from the opening 126. As shown in FIG. 10A, first and secondprobes 134, 136 are positioned, respectively, within the openings 128A,128B. In some example embodiments having a body such as body 120, atleast one additional probe may be positioned in the body 120.

FIG. 9 is a perspective sectional view of a rectangular prism-shapedwaveguide body 140 according to a sixth example embodiment. Body 140includes dielectric material having a dielectric constant greater thanabout 2, for example, alumina. In some example embodiments, thedielectric material may have a dielectric constant in the range of from2 to 10 or any range subsumed therein, or a dielectric constant in therange from 2 to 20 or any range subsumed therein, or a dielectricconstant in the range from 2 to 100 or any range subsumed therein, or aneven higher dielectric constant. In some example embodiments, the bodymay include more than one such dielectric material resulting in aneffective dielectric constant for the body within any of the rangesdescribed above. Body 140 has opposed planar first and second outersurfaces 140A, 140B (not shown), respectively, orthogonal to opposed,planar third and fourth outer surfaces 140C, 140D. Body 140 has a planarupper surface 140U from which depends downwardly an upper recess 142determined by a circumferential surface 142S and a planar bottom surface142B. Body 140 further has a planar lower surface 140L from whichdepends upwardly a lower recess 144 determined by a circumferentialsurface 144S and a planar top surface 144T. An opening 146, determinedby a circumferential surface 146S and effectively forming a lampchamber, extends between surfaces 142B and 144T so that the opening 146is in communication with recesses 142 and 144. Surfaces 142S, 146S and144S are cylindrical; however, other symmetric shapes such as square orrectangular prisms, and asymmetric shapes may be used. The axis ofsymmetry of body 140 coincides with that of upper recess 142, opening146 and lower recess 144, but body configurations with offset axes alsoare feasible. Surfaces 140A, 140B, 140C, 140D and/or 140U and 140L maybe coated with an electrically conductive coating, such as silver paintor other metallic coating as described above, as may surfaces_142S and142B of upper recess 142, surface 146S of opening 146, and surfaces 144Sand_144T of lower recess 144. First and second openings 148A, 148Bextend from surface 140L into body 140, on opposite sides of lowerrecess 144. As shown in FIG. 10B, a cross-sectional view of body 140taken along line 10B-10B of FIG. 9, a plasma bulb 150 may be positionedwithin opening 146. The plasma bulb 150 may have an outer surface 150Swhose contour matches that of surface 146S and is separated from thesurface 146S by a layer 152 of heat-sintered alumina powder or adhesive.Layer 152 may be used to optimize thermal conductivity between the bulbsurface 150S and the waveguide body 140. Alternatively, surfaces 146Sand 150S may be separated by an air-gap. Bulb 150 has upper and lowerends 150U, 150L which extend, respectively, above bottom surface 142B ofupper recess 142 and below top surface 144T of lower recess 144. Thus,in this example embodiment the bulb ends 150U, 150L are not exposed tothe highest temperatures generated by the plasma or to regions ofintensified electric field. As described above, the lower recess 144 mayalso be filled in some example embodiments while maintaining electricalseparation from the waveguide body 140. As shown in FIG. 10B, first andsecond probes 152, 154 are positioned, respectively, within openings148A, 148B. In some example embodiments having a body such as body 140,at least one additional probe may be positioned in the body 140.

As depicted schematically in FIG. 10C, a plasma lamp PL5, PL6 accordingto the fifth or sixth example embodiment, respectively, includes anamplifier AM3 whose output is connected to the first (drive) probe andwhose input is connected to the second (feedback) probe through anactive phase-shifter PS3 which modifies the phase of the signal from thesecond probe The amplifier AM3 and phase-shifter PS3 may be controlledby a microprocessor MP3 or other controller which coordinates the lampstartup and shutdown sequences and optimizes the loop phase duringstartup. In example embodiments, the amplifier AM3 may generate power ata frequency in the range of about 50 MHz to about 30 GHz or any rangesubsumed therein.

In example embodiments, the bulb 130, 150 may have any of theconfigurations and dimensions described above in connection with FIGS.4D-K with each bulb end protruding from the opening or at least one ofthe bulb ends protruding from the opening. In example embodiments, thebulb 130, 150 may extend beyond the surfaces of the waveguide body by anamount between 10 percent and 100% of the bulb inner length or any rangesubsumed therein. In example embodiments, the protrusions are equal inlength and in a range between 1 and 10 mm or any range subsumed therein.In these examples, the length of the protrusion is the distance from thecenter of the bulb where it intersects the plane of the outer surface ofthe waveguide body to the inner surface of the distal end of the bulbthat protrudes from the waveguide body. In other example embodiments,the bulb ends do not protrude from the opening or each end may protrudeby a different amount or only one end of the bulb may protrude from thewaveguide body. In example embodiments where the opening does not extendall the way through to the recess, the bulb may protrude just from thetop surface of the waveguide body. The above dimensions are examplesonly and it will be appreciated that other dimensions and bulbconfigurations may be used in other example embodiments. In a particularexample, the thickness of the waveguide adjacent to the bulb is 3 mm,the bulb has an inner length of 9 mm and extends beyond the top surfaceof the waveguide body by about 3.5 mm internal. The other end of thebulb extends below the bottom surface of the waveguide body (into therecess) by about 2.5 mm internal. This example bulb may have an outerheight of 14 mm, an outer width of 6 mm and an inner volume that iscloser to the top by 1 mm than the bottom (e.g., the thickness of thewall at the lower hemisphere may be about 3 mm thick and the thicknessof the wall at the top may be about 2 mm thick). In this example, bothends of the bulb protrude by about 5.5 mm of the outer length. Inanother example, the thickness of the waveguide adjacent to the bulb is2 mm, the bulb has an inner length of 4 mm and extends beyond the topand bottom surface of the waveguide body by about 1 mm on each end.

FIG. 11 shows dimensional parameters used in finite element model (FEM)simulations of the electric field distribution in the waveguide body 40,60, 80, 100 of FIG. 2, 3, 5 or 6 respectively. For cylindrical waveguidebody 40, H₁ (which is shown to be equal to H₂) is its height and D itsdiameter; h₀ and h₁ are the diameters of cylindrical recess 44 andcylindrical opening 42, respectively; g₀ is the thickness of dielectricmaterial between upper surface 40U and recess top 44T; and g₁ is thethickness of dielectric material between chamber bottom 42B and recesstop 44T. For rectangular prism-shaped body 60, H₁ (which is shown to beequal to H₂) is its height and D the length of the diagonal of itshorizontal cross-section; h₀ and h₁ are the lengths of the diameters ordiagonals of cylindrical or square recess 64 and cylindrical or squareopening 62, respectively; g₀ is the thickness of dielectric materialbetween upper surface 60U and recess top 64T; and g₁ is the thickness ofdielectric material between chamber bottom 62B and recess top 64T. Forcylindrical body 80 and rectangular prism-shaped body 100, g₁=0 as theopenings 84, 104 extend to the recesses 82, 102. In example embodiments,the height H₁ may differ from the H₂. The thickness, g₀, is shown to beless than the first height, H1 and the second height, H2.

Finite element modeling simulations were performed of the electric fieldintensity distribution in the waveguide bodies 40, 60, 80, 100, varyingthe FIG. 11 dimensional parameters and using software tools such asHFSS™, available from Ansoft, Inc. of Pittsburgh, Pa., and FEMLAB™,available from COMSOL, Inc. of Burlington, Mass. FEM simulation of theelectromagnetic field in a dielectric body entails first specifying: (a)the geometric dimensions, dielectric properties, and conducting surfacesof the body; (b) the probe locations and applied excitation fields; and(c) the boundary conditions at the body and free-space conditions.Mesh-size parameters controlling the simulation are then adjusted toachieve consistent results. We have found that excellent correlationbetween predicted and observed resonant frequencies can be obtained withan FEM model that ignores the electrical properties of the plasma andthus with the bulb region modeled as empty space. We also found thathigher electric field intensities occur in bodies 80 and 100 than inbodies 40 and 60. Specifically, the intensity increases as the layer ofdielectric material separating the opening from the recess decreases.FIG. 12A shows the FEM-simulated electric field intensity distributionin cylindrical waveguide body 80, resonating at the body's fundamentalmode frequency, for the combination of FIG. 11 dimensional parametersfound to provide the highest electric field intensity at 900 MHz: D=41.2mm; H=17.8 mm; h₀/D=0.33; h₁=6.15 mm; g₀=3 mm; and g₁/g₀=0. The electricfield intensity is rotationally symmetric about a vertical axis. Thelength and number density of the electric field vectors denote relativeintensity. FIG. 12B shows the FEM-simulated electric field intensitydistribution in waveguide body 80, resonating at the body's fundamentalmode frequency, for the combination of FIG. 11 dimensional parametersfound to provide the highest electric field intensity at 2.15 GHz:D=29.4 mm; H=7.62 mm; h₀/D=0.28; h₁=6.15 mm; g₀=3 mm; and g₁/g₀=0. Theabove dimensions are examples only. For example, in other exampleembodiments dimensions for these parameters in the following ranges (orany ranges subsumed therein) may be used: D (10 to 60 mm); H (3 to 30mm); h₀/D (0.10 to 0.50); h₁ (3 to 10 mm); g₀ (1 to 10 mm); and g₁/g₀ (0to 3.0). Other example embodiments may use different dimensions.

As shown in FIGS. 12A and 12B, the example waveguide body 80 may havethree regions, a first region 80A, a second region 80B and a thirdregion 80C. The second region 80B above recess 82 is thinner and has asmaller volume than the first and third regions 80A and 80C. The firstand third regions 80A, 80C may be contiguous and form a peripheralregion surrounding the second region 80B (which may be a thin region inthe middle of the waveguide body 80) as can be seen in FIGS. 5, 6, 8 and9. In this example, the height, H, of the first and third regions 80A,80C is greater than the thickness, g₀, of the second region 80B (seeFIG. 11). For example, the height, H, may be more than twice thethickness, g₀. Drive probe 92 is shown positioned in the first region80A. An opening 84 (see FIGS. 5 and 7A) may be formed in the secondregion 80B and a bulb 90 may be positioned in the opening 84. A feedbackprobe 94 may be positioned in region 80C (see FIGS. 5 and 7A) on theopposite side from the drive probe 92. Opening 84, bulb 90 and feedbackprobe 94 are omitted in FIGS. 12A and 12B for clarity. At bothfrequencies the effect of the recess 82 is to intensify the electricfield in the second region 80B where the plasma bulb 90 is located.Power is provided by the drive probe 92 in the first region 80A, whichis larger and has a lower electric field intensity. The electric fieldbecomes more concentrated in the narrow second region 80B adjacent tothe location of the bulb 90. Electric field intensity is greater than ina solid dielectric constant cylinder of the same dimensions, resultingin a lower fundamental mode frequency.

FIG. 13A shows example dependence of the fundamental mode frequency (inMHz) of an alumina waveguide body 80 to the dimensional parameter g₀ (inmm), for the following example fixed body dimensions: D=41.15 mm;H=17.78 mm; h₀=13.36 mm; and h₁=6.15 mm. The frequency is seen todecrease approximately linearly with decreasing g₀ and thus withincreasing depth of recess 82. So for a given body configuration, thechoice of g₀ can be used to tune the resonant frequency. For a solidcylindrical waveguide body the fundamental mode and its resonantfrequency are largely independent of cylinder height, because thedominant boundary condition is determined by the cylindrical surface.The fundamental and higher mode frequencies depend most directly oncylinder diameter; or, for a rectangular prism-shaped body, on thecross-section diagonal. However, waveguide bodies such as the examplebodies 40, 60, 80, 100, 120 and 140 introduce additional boundaryconditions affecting the resonant frequency.

FIG. 13B shows example dependence of the fundamental mode frequency ofan alumina waveguide body 80 to dimensional parameter g₀, for thefollowing example fixed body dimensions: D=29.36 mm; H=7.62 mm; h₀=8.13mm; and h₁=6.15 mm. Again, the fundamental mode frequency decreasesapproximately linearly with decreasing g₀. These results demonstratethat waveguide bodies according to example embodiments, even when madeof material having a dielectric constant less than 10 (such as alumina),can have volumes smaller than 6 cm³ and 23 cm³, respectively, in plasmalamps operating at 2.15 GHz and 900 MHz. It is also believed thatwaveguide bodies in example embodiments can have volumes less than 3 cm³and 11.5 cm³, respectively, in plasma lamps operating at 2.15 GHz and900 MHz when made of a material having a dielectric constant less than20.

For solid cylindrical and rectangular prism bodies, the fundamental modeand its resonant frequency are largely independent of body height(corresponding to H in FIG. 11). The most significant boundaryconditions are the side surface(s); therefore, the resonant frequenciesdepend most directly on cylinder diameter and prism diagonal. Cut-outssuch as a lower recess or upper and lower recesses introduce additionalboundary conditions which affect the resonant frequency; as alreadynoted, g₀ appears to be a significant dimensional parameter.

As described above, example embodiments may use a shaped waveguide bodyto allow operation at a lower frequency (or at the same frequency with abody of smaller volume) than a solid cylindrical or rectangularwaveguide body having the same dielectric constant. The waveguide bodymay have a region containing a bulb that is relatively thin (e.g., theregion having a height g₀ in FIG. 11), and other regions that arethicker (e.g., the region having a height H in FIG. 11). The thickerregions may be peripheral to the thin region and form a recess (e.g.,recess 44 or 64 in FIG. 2 or 3) on one side of the thin region. In someexample embodiments, the thicker regions may extend beyond the thinregion in more than one direction and form a recessed region on bothsides of the thin region (e.g., recesses 142 and 144 in FIG. 10B).Probes may be positioned in the thicker regions while the bulb ispositioned in the thin region. As shown in FIGS. 12A and 12B, theelectric field is intensified in the thin region adjacent to the bulbwhich allows operation at a lower frequency than a solid cylindrical orrectangular waveguide body having the same volume and same dielectricconstant.

For example, simulations demonstrate that in example embodiments ashaped waveguide body with a dielectric constant less than 10 and aheight of about 7.5 mm may operate in the fundamental mode at afrequency of 2.3 GHz or less and have a volume less than 3.5 cm³. Incontrast, a solid cylindrical or rectangular waveguide body with adielectric constant less than 10 and operating in the fundamental modeat a frequency of 2.3 GHz or less would be expected to have a volume ofat least 6 cm³.

Simulations also demonstrate that example embodiments with a shapedwaveguide body with a dielectric constant less than 10 and a height ofabout 18 mm may operate in the fundamental mode at a frequency of 1 GHzor less and have a volume less than 20 cm³. In contrast, a solidcylindrical or rectangular waveguide body with a dielectric constantless than 10 and operating in the fundamental mode at a frequency of 1GHz or less would be expected to have a volume of at least 30 cm³.

Generally, the resonant frequency of solid rectangular and cylindricalwaveguides of the type shown in FIGS. 1A and 1B, respectively, scaleinversely to the square root of the dielectric constant of the waveguidebody. Generally, for a constant height, the resonant frequency scalesinversely as a function of diameter or diagonal, when the diameter ordiagonal is larger than about four times the height. Thus, the volume ofa solid rectangular or cylindrical waveguide body of the type shown inFIGS. 1A and 1B is expected to scale in inverse proportion to thedielectric constant when the height is held constant. That is, tomaintain the same resonant frequency as the dielectric constant doubles,the volume must be approximately halved.

Example embodiments using a shaped waveguide are believed to be capableof resonating in a fundamental mode for a given frequency (e.g., 2.15GHz or 900 MHz) at a volume smaller than the volume required for a solidcylindrical or rectangular waveguide of the same dielectric constant toresonate in the fundamental mode at the same frequency. In some exampleembodiments, the volume of the shaped waveguide may have a volume thatis less than the volume of the corresponding solid or cylindricalwaveguide body by 10%, 20%, 30% or more.

FIGS. 15A through 23B compare the fundamental mode frequencies of theexample waveguide bodies 80 and 100 with solid rectangular-prism andcylindrical bodies of the type shown in FIGS. 1A and 1B, designed foroperation at 1 GHz and 2 GHz, as a function of body diagonal (ordiameter) and volume. The waveguide bodies may also be compared based onthe maximum distances between any two points in the waveguide body.

FIG. 14A shows a cross section 1402A of the shaped waveguide body 80 ofFIG. 5. The cross section is taken at a position orthogonal to height,H, and passes through the recess 82. The diameter is shown at 1404A. Inthis example, this is also the maximum distance between any two pointsin the cross section. A similar cross section may be taken through acylindrical waveguide body of the type shown in FIG. 1B. The diameterfor each cross section of a cylindrical body of this type is the same.For comparison of waveguide bodies having other shapes, the crosssection may be taken at particular positions within the waveguide body.For example, a cross section may be taken at a position orthogonal tothe end of the drive probe or orthogonal to the bottom or middle of thebulb. In some examples, a central axis may be defined through the bulb(in the same direction as the central axis of the light that is radiatedout of the bulb and away from the waveguide body). The cross section maybe taken orthogonal to the central axis through the bulb. In particular,the cross section with the largest diameter (or, more generally, thecross section having the largest distance between any two points) thatis orthogonal to the central axis of the bulb may be selected forcomparison purposes.

FIG. 14B shows a cross section 1402B of the shaped waveguide body 100 ofFIG. 6. The cross section is taken at a position orthogonal to height,H, and passes through the recess 102. The diagonal is shown at 1404B. Inthis example, this is also the maximum distance between any two pointsin the cross section. A similar cross section may be taken through arectangular waveguide body of the type shown in FIG. 1A. The diagonalfor each cross section in a rectangular prism of this type is the same.For comparison of waveguide bodies having other shapes, the crosssection may be taken at particular positions within the waveguide body.For example, a cross section may be taken at a position orthogonal tothe end of the drive probe or orthogonal to the bottom or middle of thebulb. In some examples, a central axis may be defined through the bulb(in the same direction as the central axis of the light that is radiatedout of the bulb and away from the waveguide body). The cross section maybe taken orthogonal to the central axis through the bulb. In particular,the cross section with the largest diagonal (or, more generally, thecross section having the largest distance between any two points) thatis orthogonal to the central axis of the bulb may be selected forcomparison purposes.

FIG. 14C shows a three dimensional representation of the outerboundaries of the shaped waveguide body 80 of FIG. 5. The distance fromthe bottom right edge of the cylinder to the top opposite edge is shownat 1450A in FIG. 14C. In this example, this is also the maximum distancebetween any two points in the three-dimensional waveguide body. Forcomparison of waveguide bodies having other shapes, the maximum distancebetween any two points in the waveguide body may be selected.

FIG. 14D shows a three dimensional representation of the outerboundaries of the shaped waveguide body 100 of FIG. 6. The distance fromthe bottom left corner right edge of the prism to the opposite top rightcorner is shown at 1450B in FIG. 14D. In this example, this is also themaximum distance between any two points in the three-dimensionalwaveguide body. For comparison of waveguide bodies having other shapes,the maximum distance between any two points in the waveguide body may beselected.

One way of comparing waveguide bodies is to look at the ratio of thediameter or diagonal of a cross section over the wavelength. Moregenerally, the maximum distance between two points in a cross sectionmay be used. This is a useful way of representing the size of a crosssection required for a particular frequency. The wavelength is equal tothe speed of light divided by the product of the fundamental frequencyand square root of the dielectric constant: C/(f*√∈_(r)). If more thanone dielectric material is used in the waveguide body, the effectivedielectric constant can be used.

FIG. 15A is a graph showing the ratio of diameter over wavelength as afunction of frequency for shaped waveguides according to exampleembodiments and for a cylindrical waveguide. In this graph, a dielectricconstant of 10 was used. The curve shown at 1502 shows the ratio ofdiameter over wavelength for a cylindrical waveguide of the type shownin FIG. 1B with a height of 12.5 mm. The curve at 1504 shows thetheoretical ideal for an infinite pill-like cylinder and “perfectmagnetic conductor” boundary approximation. This curve has adiameter/wavelength ratio of about 0.7655. The curve at 1506 shows theratio of diameter over wavelength for a shaped waveguide body 80 that isdesigned for operation at 2 GHz. In this example, the height, H, is 7.5mm, the diameter of the recess has is 10 mm and g₀ is 3 mm. As can beseen from the graph, the ratio of diameter to wavelength is less than0.7655 at frequencies over 1 GHz and is less than 0.7 for frequenciesfrom 1.5 to 2.3 GHz. The curve at 1508 shows the ratio of diameter overwavelength for a shaped waveguide body 80 that is designed for operationat 900 MHz. In this example, the height, H, is 18 mm, the diameter ofthe recess is 10 mm and g₀ is 3 mm. As can be seen from the graph, theratio of diameter to wavelength is less than 0.7655 at frequenciesbetween 600 MHz and 1.2 GHz. The ratio is less than 0.5 from 800 MHz to1.2 GHz and less than 0.4 from 1 GHz to 1.2 GHz.

FIG. 15B is a graph showing the ratio of diagonal over wavelength as afunction of frequency for shaped waveguides according to exampleembodiments and for a rectangular waveguide. In this graph, a dielectricconstant of 10 was used. The curve shown at 1552 shows the ratio ofdiagonal over wavelength for a rectangular waveguide of the type shownin FIG. 1A with a height of 12.5 mm and a 2:3 aspect ratio. The curve at1554 shows the ratio of diameter over wavelength for a shaped waveguidebody 100 that is designed for operation at 2 GHz. In this example, theheight, H, is 7.5 mm, the diameter of the recess is 10 mm, g₀ is 3 mmand the aspect ratio is 2:3. As can be seen from the graph, the ratio ofdiagonal to wavelength is less than 1.1 for frequencies from 1 to 2.3GHz and less than 1 for frequencies from 1.5 to 2.3 GHz. The curve at1556 shows the ratio of diameter over wavelength for a shaped waveguidebody 100 that is designed for operation at 900 MHz. In this example, theheight, H, is 18 mm, the diameter of the recess is 10 mm, g₀ is 3 mm andthe aspect ratio is 2:3. As can be seen from the graph, the ratio ofdiagonal to wavelength is less than 0.9 at frequencies between 600 MHzand 1.2 GHz. The ratio is less than 0.7 from 800 MHz to 1.2 GHz and lessthan 0.6 from 1 GHz to 1.2 GHz.

As shown in FIGS. 15A and 15B, a shaped waveguide can be used to achievesmaller diameters or diagonals (and, more generally, a smaller maximumdistance between any two points in a cross section) than a solidcylindrical or rectangular waveguide of comparable dimensions. Similarratios can be used to determine the ratio of the maximum distancebetween any two points in the three dimensional waveguide body (seeFIGS. 14C and 14D) over the wavelength. At the heights used, this doesnot change the ratios by a significant amount. See example tables 1-4below for differences between diameter or diagonal and the maximumdistance between any two points in the three dimensional waveguide body(indicated by the column “max dist”). As will be apparent this resultsin ratios (maximum distance between any two points in waveguide overwavelength) that are smaller for the shaped waveguides than a comparablesolid cylindrical or rectangular waveguide. Accordingly, exampleembodiments may be characterized by using the ratio of maximum distanceover wavelength for any of the maximum distances or ranges of maximumdistances described in tables 1-4 (or calculated from any of the otherexamples disclosed herein) and the corresponding fundamental frequenciesor ranges of fundamental frequencies for those example waveguides. Theratios described above would be about the same if maximum distance isused when the height, H, is 7.5 mm (see tables 1 and 2 below). Forexample, a shaped waveguide body 80 with height 7.5 mm may have ratiosof max dist/wavelength of less than 0.7 for frequencies from 1.5 to 2.3GHz. A shaped waveguide body 100 with height 7.5 mm may have ratios ofmax dist/wavelength of less than 1 for frequencies from 1.5 to 2.3 GHz.For a height of 18 mm, the ratios would be about the same at largerdiameters/diagonals (e.g., 1.6% larger at a diameter of 10 cm) whilethere is a more significant difference at smaller diameters/diagonals(e.g., about 23% larger at a diameter of 2.5 cm) (see tables 3 and 4).For example, a shaped waveguide body 80 with height 18 mm may haveratios of max dist/wavelength of less than about 0.6 for 800 MHz to 1.2GHz and less than about 0.5 from 1 GHz to 1.2 GHz. A shaped waveguidebody 100 with height 18 mm may have ratios of max dist/wavelength ofless than about 0.8 from 800 MHz to 1.2 GHz and less than about 0.7 from1 GHz to 1.2 GHz. These ratios are significantly lower than ratios for asolid cylindrical or rectangular waveguide of comparable dimensions atthe same operating frequencies.

FIG. 16A compares, as a function of body diameter, the fundamental modefrequency (in GHz) of a highly-pure alumina body 80 (asteriskdata-points) with that of a highly-pure alumina body FIG. 1B cylindricalbody (“x” data-points) for the following example conditions: a commonheight (7.5 mm) and body diameter, and for body 80 a centered circularrecess 10 mm in diameter, and a g₀ of 3 mm. The body height and diameterwere selected for a lamp designed to operate at about 2 GHz. While FIGS.16A, 16B, 17A and 17B also compare body 80 with a cylindrical body ofFIG. 1B when operating at frequencies as high as 3.5 GHz and as low as0.75 GHz, the distinctions between body 80 and the cylindrical body ofFIG. 1B are more significant at higher frequencies such as 2 GHz andless significant at lower frequencies such as 900 MHz. However, in otherexample embodiments where the body height and diameter are selected tooperate at about 900 MHz, significant differences are observed at lowerfrequencies as described below in connection with FIGS. 20A, 20B, 21A,21B. In FIG. 16A, the difference between the two diameters increaseswith increasing body fundamental frequency. For example, for afundamental frequency of 2 GHz the diameter of body 80 is about 3centimeters (cm) while the diameter of the conventional FIG. 1 body is 4cm; for a fundamental frequency below 1 GHz the diameters are about thesame. The end data-point on the body 80 curve shows that for afundamental frequency of about 2.3 GHz, the diameter is about 2.2 cm.FIG. 16B shows the FIG. 16A data in terms of the ratio of the two bodydiameters (FIG. 1B/body 80) as a function of fundamental mode frequency.

FIG. 17A compares, as a function of body volume, the fundamental modefrequency of the FIG. 16A body 80 with that of the FIG. 16A cylindricalbody under the FIG. 16A conditions. The difference between the twovolumes increases with increasing fundamental mode frequency. For afundamental frequency of 2 GHz this difference is about 4.3 cm³, avolume reduction of about 45%. For fundamental frequencies of 1.6 GHzand 2.3 GHz, the volume reduction is about 33% and 50%, respectively.The end data-point on the body 80 curve shows that for a fundamentalfrequency of about 2.3 GHz, the volume is about 3.5 cm³. FIG. 17B showsthe FIG. 17A data in terms of the ratio of the two body volumes (FIG.1B/body 80) as a function of fundamental mode frequency.

Table 1 compares the fundamental mode frequency (GHz) and volume (cm³)of body 80 and the solid cylindrical body as a function of body diameter(cm). The volumes for the cylindrical body are slightly less for a givendiameter than the volumes for body 80 with the same diameter, becausedifferent assumptions were made about the bulb volumes for the two typesof waveguides (which were subtracted from the overall volume todetermine the volumes below). As described above, example embodimentsmay use a smaller, protruding bulb (which subtracts less volume from thewaveguide body) rather than a larger bulb fully embedded in thewaveguide body. However, this is not believed to change the overallconclusions about the decrease in volumes that can be achieved at agiven frequency by using a shaped waveguide.

TABLE 1 cylindrical body body 80 diameter max dist frequency volumefrequency volume 2.5 2.61 3.4120 3.1789 2.3328 3.2127 3.0 3.09 2.74604.7988 2.0178 4.8326 3.5 3.57 2.2965 6.7132 4.0 4.07 1.9870 8.92211.6116 8.9559 5.0 5.06 1.5640 14.2236 1.3456 14.2573 6.0 6.05 1.293620.7031 1.1582 20.7369 7.0 7.04 1.1030 28.3607 1.0132 28.3945 8.0 8.040.9629 37.1965 0.9004 37.2302 9.0 9.03 0.8542 47.2103 0.8055 47.244110.0 10.03 0.7680 58.4022 0.7334 58.4360

FIG. 18A compares, as a function of body cross-section diagonal, thefundamental mode frequency of a highly-pure alumina body 100 with thatof a highly-pure alumina FIG. 1A rectangular prism-shaped body for thefollowing conditions: a common height (7.5 mm) and cross-section aspectratio of 2:3, and for body 100 a centered circular recess 10 mm indiameter, and a g₀ of 3 mm. The body height and cross-section diagonalwere selected for a lamp designed to operate at about 2 GHz. Thedifference between the two diagonals increases moderately withincreasing body fundamental frequency. For a fundamental frequency of 2GHz the body 100 diagonal is about 4.8 cm while the diagonal of the FIG.1 body is about 5.2 cm. The end data-point on the body 100 curve showsthat for a fundamental frequency of about 2.3 GHz, the diagonal is about3.6 cm. FIG. 18B shows the FIG. 15A data in terms of the ratio of thetwo body diagonals (FIG. 1A/body 100) as a function of fundamental modefrequency.

FIG. 19A compares, as a function of body volume, the fundamental modefrequency of the FIG. 18A body 100 with that of the FIG. 18A rectangularprism-shaped body under the FIG. 18A conditions. Again, the differencebetween the two volumes increases with increasing fundamental modefrequency. For a fundamental frequency of 2 GHz this difference is about43%, slightly less than for the cylindrical body comparison shown inFIG. 17A. For fundamental frequencies of 1.6 GHz and 2.3 GHz, the volumereduction is about 30% and 48%, respectively, again slightly less thanfor the cylindrical bodies. The end data-point on the body 100 curveshows that for a fundamental frequency of about 2.3 GHz, the volume isabout 4.2 cm³. FIG. 19B shows the FIG. 19A data in terms of the ratio ofthe two body volumes (FIG. 1A/body 100) as a function of fundamentalmode frequency.

Table 2 compares the fundamental mode frequency (GHz) and volume (cm³)of body 100 and the rectangular prism body as a function of bodydiagonal (cm). The volumes for the rectangular body are slightly lessfor a given diagonal than the volumes for body 100 with the samediagonal, because different assumptions were made about the bulb volumesfor the two types of waveguides (which were subtracted from the overallvolume to determine the volumes below). As described above, exampleembodiments may use a smaller, protruding bulb (which subtracts lessvolume from the waveguide body) rather than a larger bulb fully embeddedin the waveguide body (as was assumed for the rectangular body).However, this is not believed to change the overall conclusions aboutthe decrease in volumes that can be achieved at a given frequency byusing a shaped waveguide.

TABLE 2 rectangular body body 100 diagonal max dist frequency volumefrequency volume 3.606 3.68 3.273 3.997 2.313 4.031 5.408 5.46 2.0799.622 1.690 9.656 7.211 7.25 1.531 17.497 1.332 17.531 9.014 9.05 1.21627.622 1.106 27.656 10.817 10.84 1.009 39.997 0.942 40.031 12.619 12.640.863 54.622 0.819 54.656

FIG. 20A compares, as a function of body diameter, the fundamental modefrequency of a highly-pure alumina body 80 with that of a highly-purealumina FIG. 1B cylindrical body for the following conditions: a commonheight (18.0 mm) and body diameter, and for body 80 a centered circularrecess 10 mm in diameter, and a g₀ of 3 mm. The body height and diameterwere selected for a lamp designed to operate at about 1 GHz. For afundamental frequency of 1 GHz, the diameter of body 80 is about 3.8 cmwhile the diameter of the cylindrical body is about 7.3 cm, a reductionof about 48%. The end data-point on the body 80 curve shows that for afundamental frequency of about 1.1 GHz the diameter is about 3.0 cm.FIG. 20B shows the FIG. 20A data in terms of the ratio of the two bodydiameters (FIG. 1B/body 80) as a function of fundamental mode frequency,the difference between the two body diameters increasing with increasingfrequency.

FIG. 21A compares, as a function of body volume, the fundamental modefrequency of the FIG. 20A body 80 with that of the FIG. 20A cylindricalbody under the FIG. 20A conditions. The difference between the volumesincreases substantially with increasing fundamental mode frequency. Fora fundamental frequency of 1 GHz this difference is about 76%. Forfundamental frequencies of 900 MHz and 1.08 GHz, the volume reduction isabout 69% and 80%, respectively. The end data-point on the body 80 curveshows that for a fundamental frequency of about 1.1 GHz the volume isabout 5.0 cm³. FIG. 21B shows the FIG. 21A data in terms of the ratio ofthe two body volumes (FIG. 1B/body 80) as a function of fundamental modefrequency.

Table 3 compares the fundamental mode frequency (GHz) and volume (cm³)of body 80 and the solid cylindrical body as a function of body diameter(cm). As described above, different assumptions were made about the bulbvolumes for the two types of waveguides (which were subtracted from theoverall volume to determine the volumes below) although this is notbelieved to change the overall conclusions about the decrease in volumesthat can be achieved at a given frequency by using a shaped waveguide.

TABLE 3 cylindrical body body 80 diameter max dist frequency volumefrequency volume 2.5 3.08 3.241 8.434 3.0 3.50 2.609 12.321 1.084 11.433.5 3.94 2.182 16.916 4.0 4.39 1.888 22.217 0.954 21.33 5.0 5.31 1.48634.941 0.863 34.05 6.0 6.26 1.229 50.492 0.786 49.60 7.0 7.23 1.04868.870 0.733 67.98 8.0 8.20 0.915 90.076 0.679 89.18 9.0 9.18 0.811114.109 0.636 113.22 10.0 10.16 0.730 140.970 0.596 140.08

FIG. 22A compares, as a function of body cross-section diagonal, thefundamental mode frequency of a highly-pure alumina body 100 with thatof a highly-pure alumina FIG. 1A rectangular prism-shaped body for thefollowing conditions: a common height (18.0 mm) and cross-section aspectratio of 2:3, and for body 100 a centered circular recess 10 mm indiameter, and a g₀ of 3 mm. The body height and cross-section diagonalwere selected for a lamp designed to operate at about 1 GHz. For afundamental frequency of 1 GHz, the diagonal of body 100 is about 5.1 cmwhile the diagonal of the FIG. 1A rectangular prism-shaped body is about10.6 cm, a reduction of about 52% or about 4% greater than for the FIGS.20A, 20B comparison. The end data-point on the body 100 curve shows thatfor a fundamental frequency of about 1.2 GHz the diagonal is about 3.5cm. FIG. 22B shows the FIG. 22A data in terms of the ratio of the twobody diagonals (FIG. 1A/body 100) as a function of fundamental modefrequency, the difference between the two diagonals increasing withincreasing fundamental frequency.

FIG. 23A compares, as a function of body volume, the fundamental modefrequency of the FIG. 22A body 100 with that of the FIG. 22A rectangularprism-shaped body under the FIG. 22A conditions. The difference betweenthe volumes increases substantially with increasing fundamental modefrequency. For a fundamental frequency of 1 GHz this difference is about86%. For fundamental frequencies of 900 MHz and 1.08 GHz, the volumereduction is about 70% and 80%, respectively. The end data-point on thebody 100 curve shows that for a fundamental frequency of about 1.2 GHz,the volume is about 8.3 cm³. FIG. 23B shows the FIG. 23A data in termsof the ratio of the two body volumes (FIG. 1A/body 100) as a function offundamental mode frequency.

Table 4 compares the fundamental mode frequency (GHz) and volume (cm³)of body 100 and the rectangular prism body as a function of bodydiagonal (cm). As described above, different assumptions were made aboutthe bulb volumes for the two types of waveguides (which were subtractedfrom the overall volume to determine the volumes below) although this isnot believed to change the overall conclusions about the decrease involumes that can be achieved at a given frequency by using a shapedwaveguide.

TABLE 4 rectangular body body 100 diagonal max dist frequency volumefrequency volume 3.606 4.03 3.109 10.297 1.175 9.506 5.408 5.70 1.97523.797 0.983 23.006 7.211 7.43 1.454 42.697 0.853 41.906 9.014 9.191.155 66.997 0.773 66.206 10.817 10.97 0.959 96.697 0.703 95.906 12.61912.75 0.820 131.797 0.642 131.006

FIG. 24 schematically depicts a cross-sectional view of a cylindrical orrectangular prism-shaped waveguide body in a plasma lamp according to aseventh example embodiment. For simplicity, only a cylindrical body 160is described, although other shapes may be used in other exampleembodiments. Body 160 includes dielectric material having a dielectricconstant greater than about 2. In some example embodiments the materialmay have a high dielectric constant greater than 50 or even 100. In someexample embodiments the material can be magnesium calcium titanate(MCT), a ceramic having a dielectric constant of about 140. Body 160includes planar upper and lower surfaces 160U, 160L, respectively,orthogonal to a cylindrical outer surface 160S. Surfaces 160S, 160U,160L may be coated with an electrically conductive coating, such assilver paint or other metallic coating as described above. A recess 162depending from surface 160U, determined by a cylindrical surface 162S,closely receives a sleeve 164 of material having a thermal conductivitycoefficient in a range between 10 and 50 watts/meter-Kelvin. In someexample embodiments this highly thermally conductive material can bealumina. Sleeve 164 includes a planar top surface 164T approximatelylevel with body upper surface 160U, an outer surface 164S, and a planarbottom surface 164B attached to planar surface 166S of body portion 166with an adhesive such as 940HT alumina adhesive, available fromCotronics Corp. of Brooklyn, N.Y. Surface 164S is attached to surface162S by a layer 168 of alumina powder or adhesive. Alternatively,surfaces 162S and 164S are separated by an air-gap having a width in arange between 0.25 and 2 mm. An air-gap has the advantage of minimizingthe effect of thermally-induced stress between the sleeve and body.Depending from surface 164T is an opening 170, determined by acylindrical surface 170S, within which is positioned a cylindrical bulb172 having an outer surface 172S. Surface 172S is attached to surface170S by heat-sintered alumina powder or adhesive. Alternatively, anair-gap separates surfaces 170S and 172S. First and second probes 176,178 are inserted into body 160 through surface 160L. At least oneadditional probe may also be positioned in body 160. Typically, thediameter of body 160 is in a range between 1 and 6 cm, and the diameterof sleeve 164 ranges from 10% to 75% of the body diameter. By using amaterial with a high dielectric constant for the body 160 the size ofthe waveguide body may be reduced. However, the high dielectric materialmay not have desirable thermal properties (thermal expansion, thermalconductivity, consistent dielectric constant at different temperatures,etc.). By using a lower dielectric constant material with desirablethermal properties around the bulb, both a small waveguide body withhigh dielectric constant and desired thermal properties may be achieved.

FIG. 25 schematically depicts a cross-sectional view of a cylindrical orrectangular prism-shaped waveguide body in a plasma lamp according to aneighth example embodiment. Only a cylindrical body 180 is described.Body 180 includes dielectric material having a dielectric constantgreater than about 2. In some example embodiments the material can bemagnesium calcium titanate. Body 180 includes planar upper and lowersurfaces 180U, 180L, respectively, orthogonal to a cylindrical outersurface 180S. Surfaces 180S, 180U, 180L may be coated with anelectrically conductive coating, such as silver paint or other metalliccoating as described above. A first recess 182 depending from surface180U, determined by a cylindrical surface 182S, closely receives asleeve 184 of material having a thermal conductivity coefficient in arange between 10 and 50 watts/meter-Kelvin. In some example embodimentsthis highly thermally conductive material can be alumina. Sleeve 184includes a planar top surface 184T approximately level with body uppersurface 180U, an outer surface 184S, and a planar bottom surface 184Badhesively attached to planar surface 186S of body portion 186. Surface184S is attached to surface 182S by a layer 188 of alumina powder oradhesive. Alternatively, surfaces 182S and 184S are separated by anair-gap. Depending from surface 184T is an opening 190, determined by acylindrical surface 190S, within which is positioned a cylindrical bulb192 having an outer surface 192S. Surface 192S is attached to surface190S by alumina powder or adhesive. Alternatively, an air-gap separatessurfaces 190S and 192S. Body 180 further includes a second recess 200,determined by a cylindrical surface 200S and a top surface 200T,depending upwardly from surface 180L and separated from sleeve 184 bydielectric body portion 186. Surfaces 200S and 200T may be coated withan electrically conductive coating, such as silver paint or othermetallic coating as described above. First and second probes 202, 204,respectively, are inserted into body 180 through surface 180L, separatedby recess 200. At least one additional probe may also be positioned inbody 180. Typically, the diameter of body 180 is in a range between 1and 6 cm, and the diameter of sleeve 184 ranges from 10% to 75% of thebody diameter. By using a material with a high dielectric constant forthe body 180 the size of the waveguide body may be reduced. However, thehigh dielectric material may not have the thermal properties (thermalexpansion, thermal conductivity, consistent dielectric constant atdifferent temperatures, etc.). By using a lower dielectric constantmaterial with desirable thermal properties around the bulb, both a smallwaveguide body with high dielectric constant and desired thermalproperties may be achieved.

FIG. 26 shows a plasma lamp PL9 according to a ninth example embodiment.The plasma lamp has a waveguide body of solid dielectric material havinga dielectric constant greater than 2. Alumina may be used in exampleembodiments. An electrically conductive coating C, such as silver paintor other material, is shown on the surface of the waveguide body. Asimilar coating may be used in the above example embodiments, althoughit is not shown in FIG. 1-25 for ease of illustration. Another ceramicmaterial or adhesive is included around the bulb and in the recess belowthe bulb B. In this example, alumina powder may be used. The aluminapowder is packed around the bulb and into the recess and is sintered bythe heat of the bulb. The alumina powder is outside of the waveguidebody, so power can still be concentrated in a narrow region adjacent tothe bulb. While the ends of the bulb extend outside of the narrow regionof the waveguide, additional solid dielectric material (such as aluminapowder) M may be added to the lamp body outside of the boundaries of thewaveguide. This material M may provide reflection for the bulb and/orstability for the thin region of the waveguide near the bulb. Thematerial M may also be used to manage thermal properties of the lamp,such as conduction of heat from the bulb, and may be in contact withbulb surfaces that extend outside of the waveguide. The electricallyconductive coating allows irregular, complex shaped waveguides to beused while allowing the lamp body to have a different shape by includingadditional dielectric material outside the boundary of the waveguide.

As depicted schematically in FIG. 26, a plasma lamp PL9 includes anamplifier AM4 whose output is connected to the first (drive) probe DPand whose input is connected to the second (feedback) probe FP throughan active phase-shifter PS4 which modifies the phase of the signal fromthe second probe In other example embodiments, the active phase-shifterPS4 may be positioned between the output of the amplifier and the driveprobe DP rather than between the feedback probe FP and the input to theamplifier AM4. The amplifier AM4 and phase-shifter PS4 are controlled bya microprocessor MP4 or other controller which coordinates the lampstartup and shutdown sequences and optimizes the loop phase duringstartup. In example embodiments, the amplifier AM4 may generate power ata frequency in the range of about 50 MHz to about 30 GHz, or any rangesubsumed therein. A sensor S also samples the light from the bulb andprovides a signal to the microprocessor MP4 that may be used to adjustthe brightness of the lamp. This sensor may be omitted in some exampleembodiments. The microprocessor MP4 may also receive a signal from abrightness control (e.g., such as a manual setting that can be adjustedby the user) that can be used to adjust the brightness of the lamp. Thecontrol and feedback circuit shown in FIG. 26 may also be used with theother example embodiments described above.

FIG. 27A is a side view of a lamp 2700 according to an exampleembodiment. The lamp 2700 may be connected to a control and feedbackcircuit of the type shown in FIG. 26. The lamp has a connector 2702A tothe drive probe that may be connected to the output of the amplifier anda connector 2702B to the feedback probe that may be connected to theinput of the amplifier through the active phase shifter. Power iscoupled into the waveguide body 2704 to ignite a plasma in the bulb 2706as described above. As shown in FIG. 27A, the bulb 2706 may protrudefrom the front surface 2708 of the waveguide 2704 which reduces theelectric field intensity at the end of the bulb.

An example ignition and startup sequence for lamp 2700 will now bedescribed. FIG. 27B is a chart showing power coupling from inputconnector 2702A to feedback connector 2702B as a function of frequency.The curve 2740 is an approximation of the frequency response for thelamp 2700 in its cold state when the plasma in the bulb 2706 is notignited. However, as the plasma ignites, the center frequency, peakamplitude, and width of the resonance all shifts due to changingimpedance of the plasma. The positive feedback loop automaticallyoscillates at a frequency based on the load conditions and phase of thefeedback signal. If the phase is such that constructive interferenceoccurs for waves of a particular frequency circulating through the loop,and if the total response of the loop (including the amplifier, thelamp, and all connecting elements) at that frequency is such that thewave is amplified rather than attenuated in a loop-traversal, then theloop will oscillate that frequency. Because, in the absence of aphase-shifter, the phase of a wave circulating back to the same point ina loop depends on the ratio of its wavelength (frequency) to thephysical length of the loop (as well as the dielectric constants of allintervening material), whether a particular setting of the phase shifterinduces constructive or destructive feedback is itself a function offrequency. In this way, the phase shifter is used to finely-tune theactual frequency of oscillation within the range supported by the lamp'sresonant frequency response. In doing so, it also in effect tunes howwell power is coupled into the lamp, whose absorption of the incoming RFpower is itself a function of frequency. Thus the phase shifter providesa control with which the startup sequence may be optimized, as will bedescribed.

FIG. 27C is a flow chart of a method for operating a lamp 2700 accordingto an example embodiment. Referring to FIG. 27C, the lamp may be turnedon at step 2710. At step 2710, the lamp is in a cold state and theplasma is not ignited. Oscillation begins at the frequency shown at 2750in FIG. 27B. As the load conditions of the lamp change, the feedbackloop automatically adjusts the frequency and selects a frequency ofoscillation based on the resonant frequency for the load conditions andthe phase of the feedback signal. In order to spike the power toexpedite initial ignition of the plasma in the bulb, the microcontrollercause the phase shifter to adjust the phase to over couple the power asshown at step 2712 in FIG. 27C. This forces oscillation at 2752,although this is not the resonant frequency during ignition of theplasma. The “natural” oscillation would occur at the resonant frequency2754 during ignition, but the selected phase causes destructiveinterference at 2754 and constructive interference at 2752. Whilereference is made to phases selected to cause oscillation at particularfrequencies, it will be understood that the microcontroller and phaseshifter control the phase in this example embodiment and not specificfrequencies. The feedback loop automatically selects a frequency basedon load conditions and phase. The feedback loop may dynamically adjustfrequency throughout the ignition/startup process based on theseconditions, although the selected phase can shift oscillation relativeto the frequencies that would otherwise occur as the load conditionschange during ignition.

This state causes a high power level to be applied to the bulb for ashort period of time. The phase may be maintained for a first period oftime. In an example embodiment, the first period is predetermined andcontrolled by the microprocessor and may be in the range of, forexample, 50 ms to 1 second or any range subsumed therein. In aparticular example, the first period may be 100 ms. In some exampleembodiments, this state may cause the power level of the amplifier toexceed the continuous wave (CW) power rating of the amplifier for ashort period of time. For example, an amplifier with a CW power ratingof 75 watts, 100 watts or 150 watts may be used in various exampleembodiments and the power provided by the amplifier may exceed thislevel during step 2712 (by up to, for example 10%-80% more than the CWpower rating, or any range subsumed therein). The power may then belowered to a power level at or below the CW power rating in step 2714 asdescribed below. The load impedance of the lamp in this state is notwell matched to the ideal load specified for the amplifier (which maybe, for example, 50 ohms in some example embodiments). This state may bestressful on the amplifier in some example embodiments and may bemaintained for a short period of time. In some example embodiments, thefirst period of time may be selected to be less than the time specifiedfor the pulsed power rating of the amplifier. This configuration is anexample only and other configurations may be used to provide powerduring step 2712.

After the power is spiked during the first period of time, themicrocontroller causes the phase shifter to adjust the phase for asecond period of time as shown at step 2714. This causes oscillation atthe frequency shown at 2754 in FIG. 27C which is at or near the resonantfrequency during ignition. As described above, while reference is madeto particular frequencies, it will be understood that the feedback loopmay dynamically adjust frequency throughout this process. The impedancematching between the lamp and the amplifier is better than during step2712, but still may not be very good. As the plasma becomes fullyvaporized, the resonant frequency may shift to 2756 in FIG. 27B, but thephase is not adjusted for oscillation at this frequency. The secondperiod of time may be predetermined by the microcontroller and, inexample embodiments, may be between 5 and 20 seconds or any rangesubsumed therein. In a particular example, the second period of time is9.9 seconds (10 seconds less the amount of time used for step 2712).

After the second period of time, the plasma may be fully ionized asshown at step 2716 and the resonant frequency for steady state operationof the lamp may be at or near 2756. As shown at step 2718, themicrocontroller may cause the phase shifter to shift the phase tooscillate at the resonant frequency 2756 to maximize light output.

The above method is an example only and other variations may be used insome example embodiments. For example, instead of using predeterminedperiods of time set by a microcontroller or other control circuit, lampconditions (such as brightness from sensor S in FIG. 26, the signal fromthe feedback probe, a measurement of reflected power at the drive probeor other operating condition of the lamp) may be used to determine whenand how to shift the phase in some example embodiments. In other exampleembodiments, the microcontroller may step through less than four phases(for example two phases—an ignition phase and a phase for steady stateoperation when the plasma is ionized) or more than four phases (forexample a range of phases at various frequencies as the resonantfrequency changes during ignition and startup). The phase used toachieve desired lamp operating conditions during initial ignition,startup and steady state operation may be determined empirically inexample embodiments and/or through simulation/modeling and/or by signalsderived from lamp operating conditions monitored by the microprocessor.In other example embodiments, the phase selected for steady stateoperation may be slightly out of resonance, so maximum brightness is notachieved. This may be used to leave room for the brightness to beincreased and/or decreased in response to brightness control signals.

FIG. 27D is a flow chart of a method for brightness adjustment accordingto an example embodiment. This example method may be used in connectionwith a control and feedback circuit of the type shown in FIG. 26. Asshown at 2720, the microprocessor may receive a signal indicating thebrightness of the lamp should be adjusted. This signal may be generatedby a sensor S that samples the light from the bulb B. The signal mayalso be provided by a brightness control or based on timers or othertriggers in the lamp. As shown at 2722, the microcontroller then causesthe phase shifter PS4 to adjust the phase. In an example embodiment,phase shifting may be used to increase or decrease the brightness.

FIG. 28 is a cross-sectional view of a lamp PL10 with a waveguide bodyaccording to a tenth example embodiment. The lamp PL10 is similar to thelamp PL9 of FIG. 26 except that it does not have a feedback probe anduses a different power circuit. As shown in FIG. 28, an oscillator OSCmay provide power through amplifier AMS to the drive probe DP. The driveprobe DP is embedded in the solid waveguide body. A microprocessor MP5is used to control the frequency and power level provided to the driveprobe DP. The microprocessor MP5 may cause power to be provided at afirst frequency and power level for initial ignition, a second frequencyand power level for startup after initial ignition and a third frequencyand power level when the lamp reaches steady state operation. Each stepin the startup process may continue for a predetermined period of timeas determined by the microprocessor or may be based on lamp conditionssuch as a signal from sensor S or on reflected power from the waveguidebody and drive probe. Reflected power may be provided back to themicroprocessor as shown at 2802. It may be more difficult to maintainresonance with the power circuit shown in FIG. 28, because themicroprocessor must have preset conditions based on anticipated lampconditions at a particular time or must determine the settings based onconditions of the lamp. In contrast, the feedback loop of FIG. 26automatically provides dynamic adjustment of the frequency based onvarying lamp conditions.

FIG. 29 is a cross-sectional view of a lamp with a waveguide bodyaccording to an eleventh example embodiment. The lamp PL11 is similar tothe lamp PL9 of FIG. 26 except that the bulb B is formed from the lampbody. In this example embodiment, the waveguide body WG has a narrowregion adjacent to the bulb. The outer surface of the waveguide body WGhas a metallic coating C. The waveguide body WG directs power into thebulb B. A material M is added outside the waveguide body WG to definethe walls of the bulb. The material may be the same dielectric materialused for the waveguide body WG. For example, the waveguide body WG andmaterial M may both be alumina. In other example embodiments, thematerial M may be different than the waveguide body WG. For example, thematerial M may include sintered alumina powder. The material M andwaveguide body WG define a cavity extending into the lamp body from atop surface of the lamp body. A transmissive window W seals the cavityto form a bulb. The window may be quartz, sapphire or other transmissivematerial. In some example embodiments, the bulb may have a ceramic orquartz liner inside the cavity. This design allows the waveguide WG toprovide power primarily to the middle of the bulb and keep the ends ofthe bulb (including window W) away from the areas of highest electricfield intensity. Since there are no separate bulb walls in the cavity,it may be possible to design a very small bulb with high power densitywith this approach.

FIGS. 30A and 30B are perspective views of a back plate and heat sinkassembly according to an example embodiment, which provides themechanical interface for the lamp body 3002 to the rest of the system,which may include a feedback and control circuit of the type shown inFIG. 26. As described above, the outer surface of the lamp body (otherthan the surface of the waveguide adjacent to the bulb) may be coatedwith an electrically conductive material such as silver paint. The lampdielectric body 3002 and the bulb 3004 are fastened to the backplate3006, the latter also providing a cavity 3008 in the example embodimentswhere alumina powder is used as the interface between the lamp body andthe bulb. In alternative example embodiments, adhesive or othermaterials may be used as part of this interface. The interface aroundthe bulb may be important for thermal management as described furtherbelow and may be adjusted empirically or through simulation/modeling toachieve desired lamp operating conditions.

Electrical connections to the probes are made using coaxial cable to theSMA connectors 3010 and 3012, whose center pins connect to the probesthat protrude into the lamp body through holes 3022 and 3024 in the backplate. In an example embodiment, connector 3010 may connect to a driveprobe embedded in the dielectric waveguide body 3002 and connector 3012may connect to a feedback probe embedded in the dielectric waveguidebody 3002. Connector gaskets are placed between the probe-holes on thelamp-body and the backplate. These serve to both minimize EMI fromleakage at that critical juncture where guided-waves in the coaxialcable couple to the lamp, as well as regulate the thermal conductivitybetween the lamp and the backplate. The diameter, thickness, andhole-diameter are parameters that may be varied empirically to achieveboth EMI and thermal conductivity control. For example, thebackplate/gasket assembly may be configured to provide electromagneticinterference (EMI) shielding that complies with FCC part 15 class A/BEMI requirements (less than 49.5 dBuV/m at 10 meters for class A andless than 54 dBuV/m at 3 meters for class B) and also to control thermallosses to the heat sink so high brightness can be achieved (as describedfurther below). In this example, the backplate/gasket provides thedesired EMI shielding, but is not in intimate contact with the entireback side of the dielectric lamp body 3002. Thermal losses are therebylimited to avoid over cooling. A metal bracket with flanges may also beattached around the perimeter of the waveguide body to facilitateassembly of the lamp. The metal bracket may use a spring or clamp toapply positive pressure around the perimeter of the waveguide. Inexample embodiments using a metal bracket, the thermal losses from thewaveguide to the bracket may also be taken into account when managingthermal losses from the bulb.

Air-hole patterns 3018 and 3020 may also be drilled into the backplateto provide convective cooling to the lamp. The size, quantity, andplacement of these are also varied empirically to achieve the desiredoperating temperatures. The backplate may be attached to a chamber orhousing containing the waveguide and bulb. A fan may be used tocirculate air through the air holes to promote conductive and convectivecooling of the outer surfaces of the waveguide and the surfaces of thebulb exposed to the surrounding environment. In an example embodiment,air may be circulated into the chamber or housing through one set ofholes in the back plate and exhausted through a second set of holes. Inanother example embodiment, air may be circulated into both sets ofholes and exhausted through another vent or opening in the chamber orhousing containing the waveguide and bulb. The air flow may be selectedto control the rate of non-radiative heat loss from the waveguide andbulb.

Thermal losses may also be managed through the selection of the thermalconductivity of materials used in the lamp, the design of the interfacebetween the bulb and the waveguide body, the design of the interfacebetween the lamp body and the heat sink and the surface area of the bulbin contact with surrounding materials and the surface area exposed tothe surrounding environment. The bulb loses heat through conductivelosses to the surrounding materials, through conductive and convectiveheat losses to the surrounding environment and through radiation.Example embodiments may be designed to provide sufficient conductive andconvective heat transfer to avoid damage to the bulb, but otherwisemaximize radiation to provide high brightness. For example, thewaveguide may a solid alumina material.

The interface between the bulb and the waveguide may use a material witha lower thermal conductivity, such as alumina powder. In an exampleembodiment, the layer may have a thermal conductivity in the range ofabout 0.5 to 10 watts/meter-Kelvin (W/mK) or any range subsumed therein.For example, sintered alumina powder with 55% packing density (45%fractional porosity) and thermal conductivity in a range of about 1 to 2watts/meter-Kelvin (W/mK) may be used. Alternatively, a thin layer of aceramic-based adhesive or an admixture of such adhesives may be used.Depending on the formulation, a wide range of thermal conductivities isavailable. For example, one line of adhesives available commerciallyfrom Cotronics, Inc. of Brooklyn, N.Y. spans the range of 0.28 to 6.2W/mK. In one example, the Cotronics RESBOND 919 adhesive may be used.This adhesive has a thermal conductivity of about 0.58 W/mK and acontinuous-use temperature rating of 1540° C. As described above, otherexample embodiments may use a thermal layer or sleeve of material havinga thermal conductivity coefficient in a range between about 10 and 50watts/meter-Kelvin (W/mK) or any range subsumed therein. In practice,once a layer composition is selected having a thermal conductivity closeto the desired value, fine-tuning may be accomplished by altering thelayer thickness. Some example embodiments may not include a separatelayer of material around the bulb and may provide a direct conductivepath to the waveguide body.

The gaskets may be used to provide EMI shielding and a heat sink over aregion of the waveguide body. However, the back plate may be spaced bythe gaskets from the waveguide body to avoid over cooling throughconductive transfer from the waveguide body directly to the back plate.This thermal management allows a high temperature to be maintained inthe plasma in the bulb with controlled conductive losses and highradiation resulting in high brightness. While the resulting plasma mightdamage a bulb in many configurations, the bulb ends may extend beyondthe waveguide body and be spared excess damage from the plasma.Conductive and convective losses may also be managed through selectionof the bulb size. Conductive losses increase with increased size of thebulb and convective losses depend on the bulb surface area exposed tothe surrounding environment and the air flow. A very small bulb can beused to achieve a high power density and high brightness. For example, abulb with an inner width of 3 mm and an inner length of 9 mm may be usedin some example embodiments. Smaller bulbs might also be used in someexample embodiments, such as a bulb with a 3 mm inner width and 6 mminner length or a bulb with a 2 mm inner width and 4 mm inner length.The bulb may use a fill such as Indium Bromide, Sulfur, Selenium orTellurium. Additives such as Mercury may be used. In some examples, ametal halide such as Cesium Bromide may be added to stabilize adischarge of Sulfur, Selenium or Tellurium.

A waveguide comprising a dielectric material with an electricallyconductive outer coating can be used to couple power to a bulb veryefficiently as described above. The non-radiative thermal losses fromthe bulb can be controlled through by selecting the size and surfacearea of the bulb, the thermal conductivity of surrounding materials, thearea of the bulb in contact with surrounding materials, the area exposedto the external environment and the air flow and conditions maintainedin the surrounding environment.

Thermal modeling may be used to select a lamp configuration providing ahigh peak plasma temperature resulting in high brightness, whileremaining below the working temperature of the bulb material. Once ageneral model is established, the thickness of the thermal layers,positioning of the bulb and air flow may also be empirically adjusted toobtain desired lamp operating conditions. In one example, a model wasused in which the plasma region is modeled as a thermal sourcesurrounded by a region of cooler gases between the plasma and the bulbwalls. Heat is transferred to the bulb walls primarily by conduction andconvection. Between the bulb outer surface and the waveguide body (orthermal layer), there are three main heat transport paths: radiationfrom the bulb outer surface(s), convection, and conduction throughcontact with the waveguide body (or thermal layer). Of these, conductionis by far the most effective path for surfaces of the bulb in contactwith the waveguide body (or thermal layer), accounting for over 90% ofthe heat flow in the surfaces in contact with the waveguide body (orthermal layer) in one example. At the interface between the bulb outersurface(s) and the waveguide body, a thermal layer (or selection ofwaveguide materials) and surface area in contact with the bulb can beselected for fine regulation of thermal conductivity to optimize theplasma/bulb temperature ratio.

In one example, the modeling may be performed using the TAS™ softwarepackage available commercially from Harvard Thermal, Inc. of Harvard,Mass. Like other similar packages, TAS™ is based on the industrystandard SINDA (Systems-Improved Numerical Differentiating Analyzer)code. After specifying via a user interface the geometry, thermalproperties, and heat sources/sinks of the system being modeled, meshgeneration and numerical solution using a finite-difference algorithmare performed.

In one example, the plasma was modeled as a uniform tube 1 millimeter(mm) in diameter and 5 mm in length, which uniformly dissipates 120W ofheat input. The bulb was modeled as a quartz cylinder having a 5 mminner diameter and 8 mm inner length, a sidewall thickness of 2 mm, andupper and lower cap thicknesses of 2.5 mm. The waveguide body wasmodeled as a solid alumina cylinder 20 mm in height and 36 mm in outerdiameter. The top of the bulb upper cap protruded from the body's topsurface by 2.5 mm. The thermal layer (acting as a heat-flux regulator)was modeled as a layer 0.5 mm thick whose thermal conductivity wasvaried parametrically in a range between 0.05 and 1 W/mK. Forcomparison, pure single-crystal aluminum oxide has a thermalconductivity of about 40 W/mK at room temperature, while air at 400° C.has a thermal conductivity of about 0.05 W/mK. The low end of the rangemodeled therefore represents the “null” case of an air-gap between thebulb longitudinal outer surface and the opening inner surface.

In this example, a design temperature upper limit of 1200° C. wasselected for the bulb walls, several hundred degrees cooler than the1500° C. working temperature of quartz. In example embodiments, thistemperature margin can be in a range from about 100° C. to about 500°C., or any range subsumed therein. Other temperature limits may beselected for other materials. In one example, this model showed a plasmapeak temperature of about 6350° K when the thermal conductivity ofthermal layer is about 0.6 W/mK. A higher thermal conductivity wouldresult in lower bulb wall temperature at the expense of lower plasmapeak temperature and less brightness. A solid alumina waveguide body indirect contact with the bulb, with thermal conductivity in a range of 20to 40 W/mK, would result in a lower plasma temperature and lowerbrightness. On the other hand, a quartz bulb surrounded by air wouldneed to operate at lower power (with lower brightness) to keep the bulbcool enough to avoid damage to the quartz. Example embodiments using ahigher temperature material (such as a bulb having walls formed out of aportion of an alumina waveguide body) may operate at a highertemperature and permit materials with different thermal conductivity tobe used. As described above, the ends of the bulb may also extend beyondthe plasma region inside the bulb (e.g., bulbs extending beyond thesurfaces of the waveguide).

In example embodiments, use of a solid waveguide, a partial heat sink incontact with the surface of the waveguide, a material with lower thermalconductivity between the bulb and the waveguide and a small bulb mayresult in a luminous efficiency of between 80 lumens/watt and 120lumens/watt or any range subsumed therein. Example embodiments mayresult in a total brightness of between 8,000 and 12,000 lumens, or anyrange subsumed therein, or more at powers between 100-150 watts, or anyrange subsumed therein. For instance, a lamp according to an exampleembodiment may have a total brightness of more than 10,000 lumens at apower of about 100 watts. In another example, a lamp according to anexample embodiment may have a total brightness of more than 12,000lumens at a power of about 150 watts. It is believed that these resultsmay be achieved both initially and after various benchmarks, such as 100hours, 1000 hours or 10000 hours of lamp operation. In addition, damageto the bulb may be avoided by maintaining the temperature of the bulbsurfaces below the working temperature of the bulb material and byextending the ends of the bulb outside the surfaces of the waveguide(and away from the region of peak plasma temperature). For example, evenafter 100 hours, 1000 hours or 10000 hours of lamp operation at or above10000 lumens, it is believed that the above luminous efficiency andtotal brightness may be achieved without melting or significantdegradation of transmittance of the quartz (e.g., loss of 5-20% or moreof transmittance in any region of the bulb or any range subsumedtherein). These are examples only and lower or higher brightness may beachieved with other example embodiments.

The above methods may be used to control the thermal losses in bothelectrodeless bulbs and bulbs containing electrodes. A bulb may beformed from a discharge envelope of quartz, sapphire or other materialor may be formed in part by the walls of a waveguide or lamp body. Thebulb may be electrodeless and use a waveguide or coil to couple powerinto the bulb or use a pair of discharge electrodes in the bulbcomprising tungsten and/or other metals between which a discharge ismaintained. A power source provides power to the electrodes to produce adischarge. A heat sink may be placed in at least partial contact withthe bulb wall. In an example embodiment, the heat sink may be in atleast partial contact with the bulb wall around the discharge region ofthe bulb where the plasma is formed (for example, the region between theelectrodes in a bulb with electrodes). The heat sink may comprise asolid material such as a dielectric material with a dielectric constantgreater than 2. In example embodiments, alumina or alumina powder may beused. In other example embodiments, any of the thermal layer materialsdescribed above may be used. In example embodiments, the heat sink maybe a waveguide or solid lamp body or a thermal layer between a bulb anda waveguide or lamp body or a combination of the foregoing. The heatsink provides a path for conductive heat loss from the wall of the bulb.In example embodiments, the thermal conductivity may be in the range of0.5 to 50 watts/meter-Kelvin (W/mK) or any range subsumed therein. Thethermal conductivity of the heat sink and area of contact between theheat sink and bulb wall may be configured such that the wall temperatureof the bulb is maintained below a level that would damage the bulbmaterial or cause significant wall reaction between the fillingredients, the bulb material, and/or the electrode materials. Inexample embodiments, the heat sink and area of contact between the heatsink and bulb wall may be configured to enable inner bulb wall loadingsabove 1.5 W/mm² for high luminous efficacy and long lamp life. Asdescribed above, luminous efficiency of 80-120 lumens/watt or any rangesubsumed therein and high total brightness of more than 12,000 lumensmay be achieved using these thermal management techniques.

1. An electrodeless plasma lamp comprising: a lamp body comprising adielectric material having a relative permittivity greater than 2; abulb adjacent to the lamp body, the bulb containing a fill that forms aplasma when RF power is coupled to the fill from the lamp body; an RFfeed coupled to the lamp body; and a radio frequency (RF) power sourcefor coupling power into the lamp body through the RF feed and wherein ashortest distance between an end of the bulb and a point on the RF feedtraverses at least one electrically conductive material of the lampbody.
 2. The electrodeless plasma lamp of claim 1, wherein the bulb hasan exposed end from which light exits the plasma lamp, and a concealedend, the shortest distance being between the concealed end of the bulband the RF feed.
 3. The electrodeless plasma lamp of claim 1 or claim 2,wherein the RF feed is an elongate probe, the at least one electricallyconductive material including a surface which is substantially parallelto the elongate probe.
 4. The electrodeless plasma lamp of claim 3,wherein the at least one electrically conductive material iselectrically coupled to an electrically conductive coating of the lampbody.
 5. The electrodeless plasma lamp of claim 1, wherein theelectrically conductive material is spaced apart from the bulb and theRF feed.
 6. The electrodeless plasma lamp of claim 1, wherein thedistance from the end of the bulb to the end of the RF feed is less than10 mm.
 7. The electrodeless plasma lamp of claim 1, wherein the distancefrom the end of the bulb to an end of the RF feed is greater than adistance from a side of the bulb to the end of the RF feed.
 8. Theelectrodeless plasma lamp of claim 1, further comprising a dielectricmaterial between the end of the bulb and the electrically conductivematerial, the dielectric material having a lower thermal conductivitythan the lamp body.
 9. The electrodeless plasma lamp of claim 1, whereina distance from the end of the bulb to the electrically conductivematerial is less than 5 mm.
 10. The electrodeless plasma lamp of claim1, wherein the electrically conductive material is part of a circularconductive wall.
 11. The electrodeless plasma lamp of claim 1, whereinthe electrically conductive material is one of four electricallyconductive walls surrounding the end of the bulb.
 12. An electrodelessplasma lamp comprising: a lamp body comprising a dielectric materialhaving a relative permittivity greater than 2; a bulb adjacent to thelamp body, the bulb containing a fill that forms a plasma when RF poweris coupled to the fill from the lamp body; a first RF feed coupled tothe lamp body to provide radio frequency (RF) power; a second RF feedcoupled to the lamp body to obtain feedback from the lamp body; and anRF power source for coupling power into the lamp body through the firstRF feed, the RF power source configured to provide RF power at afrequency that is within the resonant bandwidth of a resonant mode forthe lamp body; wherein a distance from an end of the second RF feed to amid-point of the first RF feed traverses at least a first electricallyconductive material of the lamp body.
 13. The electrodeless plasma lampof claim 12, wherein a distance from the mid-point of the first RF feedto the first electrically conductive material is less than 5 mm.
 14. Theelectrodeless plasma lamp of claim 12, wherein a distance from an end ofthe second RF feed to a mid-point of the first RF feed traverses atleast a second electrically conductive material.
 15. The electrodelessplasma lamp of claim 14, wherein the first probe is closer to the firstelectrically conductive material than the second electrically conductivematerial and the second probe is closer to the second electricallyconductive material than the first electrically conductive material. 16.The electrodeless plasma lamp of claim 15, wherein the first probe iscloser to a central axis of the lamp body than an outer wall of the lampbody and the second probe is closer to an outer wall of the lamp bodythan a central axis of the lamp body.
 17. The electrodeless plasma lampof claim 12, wherein the resonant mode is the fundamental resonant modefor the lamp body.
 18. The electrodeless plasma lamp of claim 12,wherein the interior bulb volume is less than about 100 mm³.
 19. Theelectrodeless plasma lamp of claim 12, wherein the interior bulb volumeis less than about 50 mm³.
 20. The electrodeless plasma lamp of claim12, further comprising a drive probe.
 21. The electrodeless plasma lampof claim 20, wherein the drive probe is cylindrical with a diametergreater than 1.5 mm.
 22. The electrodeless plasma lamp of claim 20,wherein the drive probe has a length greater than 10 mm.
 23. Theelectrodeless plasma lamp of claim 20, wherein an end of the drive probeis within 3 mm of a front surface of the lamp body.
 24. Theelectrodeless plasma lamp of claim 20 wherein an end of the drive probeis more than 1.5 mm from a front surface of the lamp body.
 25. Theelectrodeless plasma lamp of claim 12, wherein RF power is provided tothe lamp body at a frequency less than 1 GHz.
 26. The electrodelessplasma lamp of claim 12, wherein the relative permittivity of the lampbody is in the range of about 9-15, the frequency of the RF power isless than about 1 GHz and the volume of the lamp body is in the range ofabout 10 cm³ to 30 cm³.